DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
General Description
The iButton®temperature/humidity logger (DS1923) is a
rugged, self-sufficient system that measures temperature
and/or humidity and records the result in a protected
memory section. The recording is done at a user-defined
rate. A total of 8192 8-bit readings or 4096 16-bit read-
ings, taken at equidistant intervals ranging from 1s to
273hr, can be stored. Additionally, 512 bytes of SRAM
store application-specific information and 64 bytes store
calibration data. A mission to collect data can be pro-
grammed to begin immediately, after a user-defined
delay, or after a temperature alarm. Access to the mem-
ory and control functions can be password protected.
The DS1923 is configured and communicates with a
host-computing device through the serial 1-Wire®proto-
col, which requires only a single data lead and a ground
return. Every DS1923 is factory lasered with a guaran-
teed unique 64-bit registration number that allows for
absolute traceability. The durable stainless-steel pack-
age is highly resistant to environmental hazards such as
dirt, moisture, and shock. Accessories permit the
DS1923 to be mounted on almost any object, including
containers, pallets, and bags.
Applications
Temperature and Humidity Logging in Food
Preparation and Processing
Transportation of Temperature-Sensitive and
Humidity-Sensitive Goods, Industrial Production
Warehouse Monitoring
Environmental Studies/Monitoring
Benefits and Features
•High Accuracy, Full-Featured Digital Temperature and
Humidity Logger Simplifies Temperature Data
Collection and Dissemination of Electronic
Temperature Record
•Digital Hygrometer Measures Humidity with 8-Bit
(0.6%RH) or 12-Bit (0.04%RH) Resolution
•Temperature Accuracy Better Than ±0.5°C from
-10°C to +65°C with Software Correction
•Measures Temperature with 8-Bit (0.5°C) or 11-Bit
(0.0625°C) Resolution
•Operating Range: -20°C to +85°C; 0 to 100% RH
(see Safe Operating Range Graph)
•Automatically Wakes Up, Measures Temperature
and/or Humidity, and Stores Values in 8kB of
Data-Log Memory in 8-Bit or 16-Bit Format
•Built-In Capacitive Polymer Humidity Sensor for
Humidity Logging
•Sampling Rate from 1s Up to 273hr
•Programmable High and Low Trip Points for
Temperature and Humidity Alarms
•Programmable Recording Start Delay After Elapsed
Time or Upon a Temperature Alarm Trip Point
•512 Bytes of General-Purpose Memory Plus
64 Bytes of Calibration Memory
•Two-Level Password Protection of All Memory and
Configuration Registers
•Individually Calibrated in a NIST-Traceable Chamber
•Calibration Coefficients for Temperature and
Humidity Factory Programmed Into Nonvolatile (NV)
Memory
•Rugged Construction Survives Harsh Environments
•Hydrophobic Filter Protects Sensor Against Dust,
Dirt, Contaminants, and Water Droplets/
Condensation with IP56 Enclosure Rating
•CE, FCC, and UL913 Certifications
•Simple Serial Port Interfaces to Most Microcontrollers
for Rapid Data Transfer
•Communicates to Host with a Single Digital Signal
Up to 15.4kbps at Standard Speed or Up to
125kbps in Overdrive Mode Using 1-Wire Protocol
•Quick Access to Alarmed Devices Through 1-Wire
Conditional Search Function
Ordering Information
Common iButton Can Features and Pin Configuration appear
at end of data sheet.
#Denotes a RoHS-compliant device that may include lead(Pb)
that is exempt under the RoHS requirements.
Examples of Accessories
PART ACCESSORY
DS9096P Self-Stick Adhesive Pad
DS9101 Multipurpose Clip
DS9093RA Mounting Lock Ring
DS9093A Snap-In FOB
DS9092 iButton Probe
PART TEMP RANGE PIN-PACKAGE
DS1923-F5# -20°C to +85°C F5 Can
19-4991; Rev 8; 3/15
iButton and 1-Wire are registered trademarks of Maxim Integrated Products, Inc.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 2www.maximintegrated.com
Absolute Maximum Ratings
Electrical Characteristics
(VPUP = +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
IO Voltage Range Relative to GND ..........................-0.3V to +6V
IO Sink Current....................................................................20mA
Operating Temperature
and Humidity Range ................-20°C to +85°C, 0 to 100%RH*
Storage Temperature
and Humidity Range ................-40°C to +85°C, 0 to 100%RH*
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
IO PIN: GENERAL DATA
1-Wire Pullup Resistance RPUP (Notes 1, 2) 2.2 k
Input Capacitance CIO (Note 3) 100 800 pF
Input Load Current ILIO pin at VPUP 6 10 μA
High-to-Low Switching Threshold VTL (Notes 4, 5) 0.4 3.2 V
Input Low Voltage VIL (Notes 1, 6) 0.3 V
Low-to-High Switching Threshold VTH (Notes 4, 7) 0.7 3.4 V
Switching Hysteresis VHY (Note 8) 0.09 N/A V
Output Low Voltage VOL At 4mA (Note 9) 0.4 V
Standard speed, RPUP = 2.2k 5
Overdrive speed, RPUP = 2.2k 2
Recovery Time
(Note 1) tREC Overdrive speed directly prior to reset
pulse, RPUP = 2.2k5
μs
Rising-Edge Hold-Off Time tREH (Note 10) 0.6 2.0 μs
Standard speed 65
Overdrive speed, VPUP > 4.5V 8
Time-Slot Duration (Note 1) tSLOT
Overdrive speed (Note 11) 9.5
μs
IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE
Standard speed, VPUP > 4.5V 480 720
Standard speed (Note 11) 690 720
Overdrive speed, VPUP > 4.5V 48 80
Reset Low Time (Note 1) tRSTL
Overdrive speed (Note 11) 70 80
μs
Standard speed, VPUP > 4.5V 15 60
Standard speed (Note 11) 15 63.5
Presence-Detect High Time tPDH
Overdrive speed (Note 11) 2 7
μs
Standard speed, VPUP > 4.5V 1.5 5
Standard speed 1.5 8
Presence-Detect Fall Time
(Note 12) tFPD
Overdrive speed 0.15 1
μs
*See the
Safe Operating Range
graph.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 3www.maximintegrated.com
Electrical Characteristics (continued)
(VPUP = +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Standard speed, VPUP > 4.5V 60 240
Standard speed (Note 11) 60 287
Overdrive speed, VPUP > 4.5V (Note 11) 7 24
Presence-Detect Low Time tPDL
Overdrive speed (Note 11) 728
μs
Standard speed, VPUP > 4.5V 65 75
Standard speed 71.5 75
Presence-Detect Sample Time
(Note 1) tMSP
Overdrive speed 8 9
μs
IO PIN: 1-Wire WRITE
Standard speed 60 120
Overdrive speed, VPUP > 4.5V (Note 11) 6 12
Write-Zero Low Time
(Notes 1, 13) tW0L
Overdrive speed (Note 11) 7.5 12
μs
Standard speed 5 15
Write-One Low Time
(Notes 1, 13) tW1L Overdrive speed 1 1.95 μs
IO PIN: 1-Wire READ
Standard speed 5 15 -
Read Low Time
(Notes 1, 14) tRL Overdrive speed 1 1.95 - μs
Standard speed tRL + 15
Read Sample Time
(Notes 1, 14) tMSR Overdrive speed tRL + 1.95 μs
REAL-TIME CLOCK (RTC)
Accuracy See RTC Accuracy graph Min/
Month
Frequency Deviation F -20°C to +85°C -300 +60 ppm
TEMPERATURE CONVERTER
8-bit mode (Note 15) 30 75
Conversion Time tCONV 16-bit mode (11 bits) 240 600 ms
Thermal Response Time
Constant RESP F5 can package (Note 16) 130 s
Conversion Error Without
Software Correction (Notes 15, 17, 18, 19) See the Temperature
Accuracy graph °C
Conversion Error with Software
Correction (Notes 15, 17, 18, 19) See the Temperature
Accuracy graph °C
HUMIDITY CONVERTER (Note 20)
Humidity Response Time
Constant RH Slow moving air (Note 21) 30 s
8 12 12 Bits
RH Resolution (Note 22) 0.64 0.04 0.04 %RH
RH Range (Note 23) 0 100 %RH
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 4www.maximintegrated.com
Electrical Characteristics (continued)
(VPUP = +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
RH Accuracy and
Interchangeability
With software correction
(Notes 18, 19, 24, 25, 26) ±5 %RH
RH Nonlinearity With software correction (Note 18) < 1
RH Hysteresis (Notes 27, 28) 0.5 %RH
RH Repeatability (Note 29) ±0.5 %RH
Long-Term Stability At 50%RH (Note 30) < 1.0 %RH/
year
Note 1: System requirement.
Note 2: Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery
times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For
more heavily loaded systems, an active pullup such as that in the DS2480B may be required.
Note 3: Capacitance on the data pin could be 800pF when VPUP is first applied. If a 2.2kΩresistor is used to pull up the data line,
2.5μs after VPUP has been applied, the parasite capacitance does not affect normal communications.
Note 4: VTL and VTH are functions of the internal supply voltage, which is a function of VPUP and the 1-Wire recovery times. The
VTH and VTL maximum specifications are valid at VPUP = 5.25V. In any case, VTL < VTH < VPUP.
Note 5: Voltage below which, during a falling edge on IO, a logic 0 is detected.
Note 6: The voltage on IO must be less than or equal to VILMAX whenever the master drives the line low.
Note 7: Voltage above which, during a rising edge on IO, a logic 1 is detected.
Note 8: After VTH is crossed during a rising edge on IO, the voltage on IO must drop by VHY to be detected as logic 0.
Note 9: The I-V characteristic is linear for voltages less than 1V.
Note 10: The earliest recognition of a negative edge is possible at tREH after VTH has been previously reached.
Note 11: Numbers in bold are not in compliance with the published iButton device standards. See the
Comparison Table
.
Note 12: Interval during the negative edge on IO at the beginning of a presence-detect pulse between the time at which the voltage
is 90% of VPUP and the time at which the voltage is 10% of VPUP.
Note 13: εin Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. The actual
maximum duration for the master to pull the line low is tW1LMAX + tF- εand tW0LMAX + tF- ε, respectively.
Note 14: δin Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high
threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF.
Note 15: To conserve battery power, use 8-bit temperature logging whenever possible.
Note 16: This number was derived from a test conducted by Cemagref in Antony, France, in July 2000:
www.cemagref.fr/English/index.htm Test Report No. E42.
Note 17: For software-corrected accuracy, assume correction using calibration coefficients with calibration equations for error
compensation.
Note 18: Software correction for humidity and temperature is handled automatically using the 1-Wire Viewer Software package
available at: www.ibutton.com.
Note 19: Warning: Maxim data-logger products are 100% tested and calibrated at time of manufacture to ensure that they meet all
data sheet parameters, including temperature and/or humidity accuracy. As with any sensor-based product, user shall be
responsible for occasionally rechecking the temperature and/or humidity accuracy of the product to ensure it is still oper-
ating properly. Furthermore, as with all products of this type, when deployed in the field and subjected to handling, harsh
environments, or other hazards/use conditions, there may be some extremely small but nonzero logger failure rate. In
applications where the failure of any logger is a concern, user shall assure that redundant (or other primary) methods of
testing and determining the handling methods, quality, and fitness of the articles and products are implemented to further
mitigate any risk.
Note 20: All humidity specifications are determined at +25°C except where specifically indicated.
Note 21: Response time is determined by measuring the 1/e point as the device transitions from 40%RH to 90%RH or 90%RH to
40%RH, whichever is slower. Test was performed at 5L/min airflow.
Note 22: All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery life-
time is the same no matter what RH resolution is logged.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 5www.maximintegrated.com
Note 23: Reliability studies have shown that the device survives a minimum of 1000 cycles of condensation and drying, but this
product is not guaranteed for extended use in condensing environments.
Note 24: Software-corrected accuracy is accomplished using the method detailed in the
Software Correction Algorithm for
Temperature
section.
Note 25: Every DS1923 device is measured and calibrated in a controlled, NIST-traceable RH environment.
Note 26: Higher accuracy versions may be available. Contact the factory for details.
Note 27: If this device is exposed to a high humidity environment (> 70%RH), and then exposed to a lower RH environment, the
device reads high for a period of time. The device typically reads within +0.5%RH at 20%RH, 30 minutes after being
exposed to continuous 80%RH for 30 minutes.
Note 28: All capacitive RH sensors can change their reading depending upon how long they have spent at high (> 70%RH) or low
RH (< 20%RH). This effect is called saturation drift and can be compensated through software, as described in the
Software Saturation Drift Compensation
section.
Note 29: Individual RH readings always include a noise component (repeatability). To minimize measurement error, average as
many samples as is reasonable.
Note 30: Like all relative humidity sensors, when exposed to contaminants and/or conditions toward the limits of the safe operating
range, accuracy degradation can result (see the
Safe Operating Range
graph). For maximum long-term stability, the sen-
sor should not be exposed or subjected to organic solvents, corrosive agents (e.g., strong acids, SO2, H2SO4, CI2, HCL,
H2S) and strong bases (i.e., compounds with a pH greater than 7). Dust settling on the filter surface does not affect the
sensor performance except to possibly decrease the speed of response. For more information on the RH sensor’s toler-
ance to chemicals visit: http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf.
Note 31: Guaranteed by design; not production tested to -20°C.
Comparison Table
LEGACY VALUES DS1923 VALUES
STANDARD SPEED
(μs)
OVERDRIVE SPEED
(μs)
STANDARD SPEED
(μs)
OVERDRIVE SPEED
(μs)
PARAMETER
MIN MAX MIN MAX MIN MAX MIN MAX
tSLOT (including tREC) 61 (undefined) 7 (undefined) 65* (undefined) 9.5 (undefined)
tRSTL 480 (undefined) 48 80 690 720 70 80
tPDH 15 60 2 6 15 63.5 27
tPDL 60 240 8 24 60 287 7 28
tW0L 60 120 6 16 60 120 7.5 12
*
Intentional change; longer recovery time requirement due to modified 1-Wire front-end.
Note: Numbers in bold are not in compliance with the published iButton device standards.
iButton Can Physical Specification
SIZE See the Package Information section.
WEIGHT Ca. 5.0 grams
Electrical Characteristics (continued)
(VPUP = +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 6www.maximintegrated.com
Safe Operating Range
0
20
40
60
80
100
HUMIDITY (%RH)
SAFE OPERATING ZONE
STORAGE
ONLY
-40 -20 0 20 40 60 80
TEMPERATURE (°C)
Temperature Accuracy
-1.0
-20-100 1020304050607080
-0.5
0
0.5
1.0
1.5
2.0
NOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.
TEMPERATURE (°C)
ERROR (°C)
UNCORRECTED MAXIMUM ERROR
UNCORRECTED MINIMUM ERROR
SW CORRECTED MAXIMUM ERROR
SW CORRECTED MINIMUM ERROR
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 7www.maximintegrated.com
Minimum Lifetime vs. Temperature, Slow Sampling (Temperature Only)
0
1
2
3
4
5
6
7
8
9
10
8-BIT MINIMUM PRODUCT LIFETIME (YEARS)
0
1
2
3
4
5
6
7
8
9
10
11-BIT MINIMUM PRODUCT LIFETIME (YEARS)
EVERY MINUTE
EVERY 60 MINUTES
EVERY 3 MINUTES
NO SAMPLES
EVERY 10 MINUTES
OSCILLATOR OFF
EVERY MINUTE
EVERY 60 MINUTES
EVERY 3 MINUTES
NO SAMPLES
EVERY 10 MINUTES
OSCILLATOR OFF
EVERY 30 MINUTES
EVERY 300 MINUTES
-20-1001020304050607080
TEMPERATURE (°C)
-20-1001020304050607080
TEMPERATURE (°C)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 8www.maximintegrated.com
Minimum Lifetime vs. Temperature, Fast Sampling (Temperature Only)
0
50
100
150
200
250
300
350
8-BIT MINIMUM PRODUCT LIFETIME (DAYS)11-BIT MINIMUM PRODUCT LIFETIME (DAYS)
EVERY SECOND
EVERY 30 SECONDS
EVERY 3 SECONDS
EVERY 60 SECONDS
EVERY 10 SECONDS
EVERY SECOND
EVERY 30 SECONDS
EVERY 3 SECONDS
EVERY 60 SECONDS
EVERY 10 SECONDS
-20-1001020304050607080
TEMPERATURE (°C)
-20-1001020304050607080
TEMPERATURE (°C)
0
20
40
60
80
100
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 9www.maximintegrated.com
0
1
2
3
4
5
6
7
8
9
10
8-BIT TEMPERATURE PLUS HUMIDITY MINIMUM
PRODUCT LIFETIME (YEARS)
EVERY MINUTE
EVERY 60 MINUTES NO SAMPLES
EVERY 3 MINUTES
OSCILLATOR OFF
EVERY 10 MINUTES
-20-1001020304050607080
TEMPERATURE (°C)
Minimum Lifetime vs. Temperature, Slow Sampling
(Temperature with Humidity)
0
50
100
150
200
250
300
350
8-BIT TEMPERATURE PLUS HUMIDITY MINIMUM
PRODUCT LIFETIME (DAYS)
EVERY SECOND
EVERY 30 SECONDS
EVERY 3 SECONDS
EVERY 60 SECONDS
EVERY 10 SECONDS
-20-1001020304050607080
TEMPERATURE (°C)
Minimum Lifetime vs. Temperature, Fast Sampling
Temperature with Humidity)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 10www.maximintegrated.com
Minimum Product Lifetime vs. Sample Rate (Temperature Only)
0.01
0.01 0.1 1 10 100
0.1
1
10
NOTE: WITH HUMIDITY LOGGING ACTIVATED, THE LIFETIME IS REDUCED BY LESS THAN 11% FOR THE SAMPLE RATES OF 3MIN. AND SLOWER, AND BY A
MAXIMUM OF 20% FOR SAMPLE RATES OF 1MIN. AND FASTER.
0°C
+40°C
+60°C
+75°C
+85°C
0°C
+40°C
+60°C
+75°C
+85°C
MINUTES BETWEEN SAMPLES
0.01 0.1 1 10 100
NOTE: WITH HUMIDITY LOGGING ACTIVATED, THE LIFETIME IS REDUCED BY A MAXIMUM OF 4%. THE INCREMENTAL ENERGY CONSUMED BY HUMIDITY
LOGGING IS INDEPENDENT OF THE HUMIDITY LOGGING RESOLUTION.
MINUTES BETWEEN SAMPLES
8-BIT MINIMUM PRODUCT LIFETIME (YEARS)11-BIT MINIMUM PRODUCT LIFETIME (YEARS)
0.001
0.01
0.1
1
10
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 11www.maximintegrated.com
RTC Accuracy (Typical)
-5.0
-4.0
-3.0
-2.0
-1.0
0.0
1.0
2.0
DRIFT (MINUTES/MONTH)
-20 -10 0 10 20 30 40 50 60 70 80
TEMPERATURE (°C)
Detailed Description
The DS1923 is an ideal device to monitor for extended
periods of time the temperature and humidity of any
object it is attached to or shipped with, such as fresh
produce, medical drugs and supplies, and for use in
refrigerators and freezers, as well as for logging climat-
ic data during the transport of sensitive objects and
critical processes such as curing. A 1.27mm diameter
hole in the lid of the device allows for air to reach the
humidity sensor. The rest of the electronics inside the
DS1923 is sealed so that it is not exposed to ambient
humidity. Note that the initial sealing level of the
DS1923 achieves the equivalent of IP56. Aging and use
conditions can degrade the integrity of the seal over
time, so for applications with significant exposure to liq-
uids, sprays, or other similar environments, it is recom-
mended to place the Hygrochron™ under a shield to
protect it (refer to Application Note 4126:
Understanding
the IP (Ingress Protection) Ratings of iButton Data
Loggers and Capsule
). The hydrophobic filter may not
protect the DS1923 from destruction in the event of full
submersion in liquid. Software for setup and data
retrieval through the 1-Wire interface is available for free
download from the iButton website (www.ibutton.com).
This software also includes drivers for the serial and USB
port of a PC and routines to access the general-purpose
memory for storing application-specific or equipment-
specific data files.
All iButton data loggers are calibrated/validated against
NIST traceable reference devices. Maxim offers a web
application to generate validation certificates for the
DS1922L, DS1922T, DS1922E, and DS1923 (tempera-
ture portion only) data loggers. Input is the iButton
device ROM code (or list of codes) and the output is a
validation certificate in PDF format. For more informa-
tion, refer to Application Note 4629:
iButton
®
Data-
Logger Calibration and NIST Certificate FAQs
.
Overview
The block diagram in Figure 1 shows the relationships
between the major control and memory sections of the
DS1923. The device has six main data components:
64-bit lasered ROM; 256-bit scratchpad; 512-byte gen-
eral-purpose SRAM; two 256-bit register pages of time-
keeping, control, status, and counter registers and
passwords; 64 bytes of calibration memory; and 8192
bytes of data-logging memory. Except for the ROM
and the scratchpad, all other memory is arranged in a
single linear address space. The data-logging memo-
ry, counter registers, and several other registers are
Hygrochron is a trademark of Maxim Integrated Products, Inc.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 12www.maximintegrated.com
DS1923
GENERAL-PURPOSE
SRAM
(512 BYTES)
CALIBRATION MEMORY
(64 BYTES)
REGISTER PAGES
(64 BYTES)
MEMORY
FUNCTION
CONTROL
64-BIT
LASERED
ROM
256-BIT
SCRATCHPAD
CONTROL
LOGIC
HUMIDITY
SENSOR AND
ADC2
32.768kHz
OSCILLATOR
3V LITHIUM
IO
THERMAL
SENSE ADC1
DATA-LOG MEMORY
8KB
INTERNAL
TIMEKEEPING,
CONTROL REGISTERS,
AND COUNTERS
ROM
FUNCTION
CONTROL
1-Wire PORT PARASITE-POWERED
CIRCUITRY
Figure 1. Block Diagram
read only for the user. Both register pages are write
protected while the device is programmed for a mis-
sion. The password registers, one for a read password
and another one for a read/write password, can only
be written, never read.
Figure 2 shows the hierarchical structure of the 1-Wire
protocol. The bus master must first provide one of the
eight ROM function commands: Read ROM, Match
ROM, Search ROM, Conditional Search ROM, Skip
ROM, Overdrive-Skip ROM, Overdrive-Match ROM, or
Resume. Upon completion of an Overdrive-ROM com-
mand executed at standard speed, the device enters
overdrive mode, where all subsequent communication
occurs at a higher speed. The protocol required for
these ROM function commands is described in Figure
11. After a ROM function command is successfully exe-
cuted, the memory and control functions become
accessible and the master can provide any one of the
eight available commands. The protocol for these
memory and control function commands is described
in Figure 9. All data is read and written least signifi-
cant bit first.
Parasite Power
The block diagram (Figure 1) shows the parasite-pow-
ered circuitry. This circuitry “steals” power whenever
the IO input is high. IO provides sufficient power as
long as the specified timing and voltage requirements
are met. The advantages of parasite power are two-
fold: 1) By parasiting off this input, battery power is not
consumed for 1-Wire ROM function commands, and
2) if the battery is exhausted for any reason, the ROM
may still be read normally. The remaining circuitry of
the DS1923 is solely operated by battery energy.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 13www.maximintegrated.com
AVAILABLE COMMANDS: DATA FIELD AFFECTED:
READ ROM
MATCH ROM
SEARCH ROM
CONDITIONAL SEARCH ROM
SKIP ROM
RESUME
OVERDRIVE-SKIP ROM
OVERDRIVE-MATCH ROM
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG, ALARM FLAGS, SEARCH CONDITIONS
RC-FLAG
RC-FLAG
RC-FLAG, OD-FLAG
64-BIT ROM, RC-FLAG, OD-FLAG
1-Wire ROM
FUNCTION COMMANDS
WRITE SCRATCHPAD
READ SCRATCHPAD
COPY SCRATCHPAD WITH PW
READ MEMORY WITH PW AND CRC
CLEAR MEMORY WITH PW
FORCED CONVERSION
START MISSION WITH PW
STOP MISSION WITH PW
256-BIT SCRATCHPAD, FLAGS
256-BIT SCRATCHPAD
512-BYTE DATA MEMORY, REGISTERS, FLAGS, PASSWORDS
MEMORY, REGISTERS, PASSWORDS
MISSION TIMESTAMP, MISSION SAMPLES COUNTER,
START DELAY, ALARM FLAGS, PASSWORDS
MEMORY ADDRESSES 020Ch TO 020Fh
FLAGS, TIMESTAMP, MEMORY ADDRESSES
020Ch TO 020Fh (WHEN LOGGING)
FLAGS
DS1923-SPECIFIC
MEMORY/CONTROL FUNCTION
COMMANDS
COMMAND LEVEL:
BUS
MASTER
1-Wire NET OTHER DEVICES
DS1923
Figure 2. Hierarchical Structure for 1-Wire Protocol
MSB
8-BIT
CRC CODE 48-BIT SERIAL NUMBER
MSB MSBLSB
LSB
LSB
8-BIT FAMILY CODE
(41h)
MSBLSB
Figure 3. 64-Bit Lasered ROM
64-Bit Lasered ROM
Each DS1923 contains a unique ROM code that is 64
bits long. The first 8 bits are a 1-Wire family code. The
next 48 bits are a unique serial number. The last 8 bits
are a cyclic redundancy check (CRC) of the first 56 bits
(see Figure 3 for details). The 1-Wire CRC is generated
using a polynomial generator consisting of a shift regis-
ter and XOR gates as shown in Figure 4. The polynomi-
al is X8+ X5+ X4+ 1. Additional information about the
1-Wire CRC is available in Application Note 27:
Understanding and Using Cyclic Redundancy Checks
with Maxim iButton Products
.
The shift register bits are initialized to 0. Then, starting
with the least significant bit of the family code, one bit
at a time is shifted in. After the 8th bit of the family code
has been entered, the serial number is entered. After
the last bit of the serial number has been entered, the
shift register contains the CRC value. Shifting in the 8
bits of CRC returns the shift register to all 0s.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 14www.maximintegrated.com
Memory
Figure 5 shows the DS1923 memory map. Pages 0 to
15 contain 512 bytes of general-purpose SRAM. The
various registers to set up and control the device fill
pages 16 and 17, called register pages 1 and 2 (see
Figure 6 for details). Pages 18 and 19 can be used as
storage space for calibration data. The data-log log-
ging memory starts at address 1000h (page 128) and
extends over 256 pages. The memory pages 20 to
127 are reserved for future extensions. The scratch-
pad is an additional page that acts as a buffer when
writing to the SRAM memory or the register pages.
The calibration memory holds data from the device
calibration that can be used to further improve the
accuracy of temperature and humidity readings. See
the
Software Correction Algorithm
sections for details.
The last byte of the calibration memory page stores an
8-bit CRC of the preceding 31 bytes. Page 19 is an
exact copy of the data in page 18. While the user can
overwrite the calibration memory, this is not recom-
mended. See the
Security by Password
section for
ways to protect the memory. The access type for the
32-BYTE INTERMEDIATE STORAGE
SCRATCHPAD
ADDRESS
0000h TO 001Fh 32-BYTE GENERAL-PURPOSE SRAM
(R/W) PAGE 0
0020h TO 01FFh GENERAL-PURPOSE SRAM (R/W) PAGES 1 TO 15
0200h TO 021Fh 32-BYTE REGISTER PAGE 1 PAGE 16
0220h TO 023Fh 32-BYTE REGISTER PAGE 2 PAGE 17
0240h TO 025Fh CALIBRATION MEMORY PAGE 1 (R/W) PAGE 18
0260h TO 027Fh CALIBRATION MEMORY PAGE 2 (R/W) PAGE 19
0280h TO 0FFFh (RESERVED FOR FUTURE EXTENSIONS) PAGES 20 TO 127
1000h TO 2FFFh DATA-LOG MEMORY (READ ONLY) PAGES 128 TO 383
Figure 5. Memory Map
1ST
STAGE
2ND
STAGE
3RD
STAGE
4TH
STAGE
7TH
STAGE
8TH
STAGE
6TH
STAGE
5TH
STAGE
X0X1X2X3X4
POLYNOMIAL = X8 + X5 + X4 + 1
INPUT DATA
X5X6X7X8
Figure 4. 1-Wire CRC Generator
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 15www.maximintegrated.com
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION ACCESS*
0200h 0 10 Seconds Single Seconds
0201h 0 10 Minutes Single Minutes
0202h 0 12/24
20 Hour
AM/PM 10 Hour Single Hours
0203h 0 0 10 Date Single Date
0204h CENT 0 0 10
Months Single Months
0205h 10 Years Single Years
Real-
Time Clock
Registers R/W R
0206h Low Byte
0207h 0 0 High Byte
Sample
Rate R/W R
0208h Low Threshold
0209h High Threshold
Temperature
Alarms R/W R
020Ah Low Threshold
020Bh High Threshold
Humidity
Alarms R/W R
020Ch Low Byte 0 0 0 0 0
020Dh High Byte
Latest
Temperature R R
020Eh Low Byte
020Fh High Byte
Latest
Humidity R R
0210h 0 0 0 0 0 0 ETHA ETLA
Temperature
Alarm
Enable
R/W R
0211h 1 1 1 1 1 1 EHHA EHLA
Humidity
Alarm
Enable
R/W R
0212h 0 0 0 0 0 0 EHSS EOSC RTC Control R/W R
0213h 1 1 SUTA RO HLFS TLFS EHL ETL
Mission
Control R/W R
0214h BOR 1 1 1 HHF HLF THF TLF Alarm Status R R
0215h 1 1 0 WFTA MEMCLR 0 MIP 0 General
Status R R
0216h Low Byte
0217h Center Byte
0218h High Byte
Start
Delay
Counter
R/W R
Figure 6. Register Pages Map
*
The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a
mission is in progress.
register pages is register-specific and depends on
whether the device is programmed for a mission.
Figure 6 shows the details. The data-log memory is
read only for the user. It is written solely under super-
vision of the on-chip control logic. Due to the special
behavior of the write access logic (write scratchpad,
copy scratchpad), it is recommended to only write full
pages at a time. This also applies to the register
pages. See the
Address Registers and Transfer
Status
section for details.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 16www.maximintegrated.com
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 FUNCTION ACCESS*
0219h 0 10 Seconds Single Seconds
021Ah 0 10 Minutes Single Minutes
021Bh 0 12/24
20 Hour
AM/PM 10 Hour Single Hours
021Ch 0 0 10 Date Single Date
021Dh CENT 0 0 10
Months Single Months
021Eh 10 Years Single Years
Mission
Timestamp R R
021Fh (No Function; Reads 00h) — R R
0220h Low Byte
0221h Center Byte
0222h High Byte
Mission
Samples
Counter
R R
0223h Low Byte
0224h Center Byte
0225h High Byte
Device
Samples
Counter
R R
0226h Configuration Code Flavor R R
0227h EPW PW Control R/W R
0228h First Byte
… …
022Fh Eighth Byte
Read
Access
Password
W —
0230h First Byte
… …
0237h Eighth Byte
Full
Access
Password
W —
0238h
…
023Fh
(No function; all these bytes read 00h) — R R
Figure 6. Register Pages Map (continued)
*
The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a
mission is in progress.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 17www.maximintegrated.com
Detailed Register Descriptions
Timekeeping and Calendar
The RTC and calendar information is accessed by
reading/writing the appropriate bytes in the register
page, address 0200h to 0205h. For readings to be
valid, all RTC registers must be read sequentially start-
ing at address 0200h. Some of the RTC bits are set to
0. These bits always read 0 regardless of how they are
written. The number representation of the RTC registers
is binary-coded decimal (BCD) format.
The DS1923’s RTC can run in either 12hr or 24hr mode.
Bit 6 of the Hours register (address 0202h) is defined
as the 12hr or 24hr mode select bit. When high, the
12hr mode is selected. In the 12hr mode, bit 5 is the
AM/PM bit with logic 1 being PM. In the 24hr mode, bit
5 is the 20hr bit (20hr to 23hr). The CENT bit, bit 7 of
the Months register, can be written by the user. This bit
changes its state when the years counter transitions
from 99 to 00.
The calendar logic is designed to automatically com-
pensate for leap years. For every year value that is
either 00 or a multiple of 4, the device adds a 29th of
February. This works correctly up to (but not including)
the year 2100.
Sample Rate
The content of the Sample Rate register (addresses
0206h, 0207h) specifies the time elapse (in seconds if
EHSS = 1, or minutes if EHSS = 0) between two tem-
perature/humidity-logging events. The sample rate can
be any value from 1 to 16,383, coded as an unsigned
14-bit binary number. If EHSS = 1, the shortest time
between logging events is 1s and the longest (sample
rate = 3FFFh) is 4.55hr. If EHSS = 0, the shortest is
1min and the longest time is 273.05hr (sample rate =
3FFFh). The EHSS bit is located in the RTC Control reg-
ister at address 0212h. It is important that the user sets
the EHSS bit accordingly while setting the Sample Rate
register. Writing a sample rate of 0000h results in a
sample rate = 0001h, causing the DS1923 to log the
temperature either every minute or every second
depending upon the state of the EHSS bit.
Sample Rate Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0206h Sample Rate Low
0207h 0 0 Sample Rate High
RTC Registers Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0200h 0 10 Seconds Single Seconds
0201h 0 10 Minutes Single Minutes
0202h 0 12/24
20 Hour
AM/PM 10 Hour Single Hours
0203h 0 0 10 Date Single Date
0204h CENT 0 0 10 Months Single Months
0205h 10 Years Single Years
Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.
Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 18www.maximintegrated.com
Latest Temperature Conversion Result Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 BYTE
020Ch T2 T1 T0 0 0 0 0 0 TRL
020Dh T10 T9 T8 T7 T6 T5 T4 T3 TRH
Temperature Conversion
The DS1923’s temperature range begins at -20°C and
ends at +85°C. Temperature values are represented as
an 8-bit or 16-bit unsigned binary number with a resolu-
tion of 0.5°C in 8-bit mode and 0.0625°C in 16-bit
mode.
The higher temperature byte TRH is always valid. In
16-bit mode, only the three highest bits of the lower
byte TRL are valid. The five lower bits all read 0. TRL is
undefined if the device is in 8-bit temperature mode. An
out-of-range temperature reading is indicated as 00h or
0000h when too cold and FFh or FFE0h when too hot.
With TRH and TRL representing the decimal equivalent
of a temperature reading, the temperature value is cal-
culated as:
ϑ(°C) = TRH/2 - 41 + TRL/512 (16-bit mode,
TLFS = 1, see address 0213h)
ϑ(°C) = TRH/2 - 41 (8-bit mode, TLFS = 0,
see address 0213h)
This equation is valid for converting temperature read-
ings stored in the data-log memory as well as for data
read from the Latest Temperature Conversion Result
register.
To specify the temperature alarm thresholds, the previ-
ous equations are resolved to:
TALM = 2 x ϑ(°C) + 82
Because the temperature alarm threshold is only one
byte, the resolution or temperature increment is limited to
0.5°C. The TALM value must be converted into hexadec-
imal format before it can be written to one of the
Temperature Alarm Threshold registers (Low Alarm
address 0208h; High Alarm address 0209h).
Independent of the conversion mode (8-bit or 16-bit),
only the most significant byte of a temperature conver-
sion is used to determine whether an alarm is generated.
Humidity Conversion
In addition to temperature, the DS1923 can log humidi-
ty data in an 8-bit or 16-bit format. Humidity values are
represented as 8-bit or 16-bit unsigned binary numbers
with a resolution of 0.64%RH in the 8-bit mode and
0.04%RH in the 16-bit mode.
The DS1923 reads data from its humidity sensor when-
ever a Forced Conversion command is executed (see
the
Memory and Control Function Commands
section)
or during a mission if the device is set up to log humidi-
ty data. Regardless of its setup, the DS1923 always
reads 16 bits from the humidity sensor. The result of the
latest humidity reading is found at address 020Eh (low
byte) and 020Fh (high byte). The most significant bit
read from the humidity sensor can always be found as
H11 at address 020Fh. Due to the 12-bit digital output
of the humidity sensor, the lower 4 bits in 16-bit format
are undefined.
Table 1. Temperature Conversion Examples
TRH TRL
MODE HEX DECIMAL HEX DECIMAL
(°C)
8-Bit 54h 84 — — 1.0
8-Bit 17h 23 — — -29.5
16-Bit 54h 84 00h 0 1.000
16-Bit 17h 23 60h 96 -29.3125
Table 2. Temperature Alarm Threshold Examples
TALM
(°C) HEX DECIMAL
25.5 85h 133
-10.0 3Eh 62
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 19www.maximintegrated.com
During a mission, if humidity logging is enabled, the
HRH byte (H11 to H4) is always recorded. The HRL
byte is only recorded if the DS1923 is set up for 16-bit
humidity logging. The logging mode (8-bit or 16-bit) is
selected through the HLFS bit at the Mission Control
register, address 0213h.
With HRH and HRL representing the decimal equivalent
of a humidity reading, the actual humidity is calculated
according to the algorithms shown in the table below.
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 BYTE
020Eh H3 H2 H1 H0 X X X X HRL
020Fh H11 H10 H9 H8 H7 H6 H5 H4 HRH
16-BIT MODE, HLFS = 1 8-BIT MODE, HLFS = 0
IVAL = (HRH x 256 + HRL)/16
Round IVAL down to the nearest integer; this eliminates the
undefined 4 bits of HRL.
(N/A)
ADVAL = IVAL x 5.02/4096 ADVAL = HRH x 5.02/256
HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307
Table 3. Humidity Conversion Examples
HRH HRL
MODE HEX DECIMAL HEX DECIMAL HUMIDITY (%RH)
8-bit B5h 181 84.41
8-bit 67h 103 34.59
16-bit B5h 181 C0h 192 84.89
16-bit 67h 103 30h 48 34.70
Table 4. Humidity Alarm Threshold Examples
HALM
HUMIDITY (%RH) HEX DECIMAL
65 97h 151
25 58h 88
Latest Humidity Conversion Result Register Bitmap
The result is a raw humidity reading that needs to be
corrected to achieve the specified accuracy. See the
Software Correction Algorithm for Humidity
section for
further details.
To specify the humidity alarm thresholds, the equation
needs to be resolved to:
ADVAL = HUMIDITY(%RH) x 0.0307 + 0.958
HALM = ADVAL x 256/5.02
Round HALM to the nearest integer.
The HALM value needs to be converted into hexadeci-
mal before it can be written to one of the Humidity Alarm
Threshold registers (Low Alarm address 020Ah; High
Alarm address 020Bh). Independent of the conversion
mode (8-bit or 16-bit), only the most significant byte of a
humidity conversion is used to determine whether an
alarm is generated. The alarm thresholds are applied to
the raw humidity readings. Therefore, if software correc-
tion is used, the effect of the software correction is to be
reversed before calculating a humidity alarm threshold.
For example, let the desired alarm threshold be 60%RH.
The 60% threshold may correspond to a raw reading of
65%RH (i.e., before correction). To set a 60%RH (after
correction) threshold, the HALM value then needs to be
calculated for 65%RH.
These examples do not include the effects of software
correction.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 20www.maximintegrated.com
Temperature Sensor Alarm
The DS1923 has two Temperature Alarm Threshold
registers (address 0208h, 0209h) to store values that
determine whether a critical temperature has been
reached. A temperature alarm is generated if the
device measures an alarming temperature and the
alarm signaling is enabled. The bits ETLA and ETHA
that enable the temperature alarm are located in the
Temperature Sensor Control register. The temperature
alarm flags TLF and THF are found in the Alarm Status
register at address 0214h.
Bit 1: Enable Temperature High Alarm (ETHA). This
bit controls whether, during a mission, the temperature
high alarm flag (THF) can be set, if a temperature con-
version results in a value equal to or higher than the
value in the Temperature High Alarm Threshold register.
If ETHA is 1, temperature high alarms are enabled. If
ETHA is 0, temperature high alarms are not generated.
Bit 0: Enable Temperature Low Alarm (ETLA). This
bit controls whether, during a mission, the temperature
low alarm flag (TLF) can be set, if a temperature con-
version results in a value equal to or lower than the
value in the Temperature Low Alarm Threshold register.
If ETLA is 1, temperature low alarms are enabled. If
ETLA is 0, temperature low alarms are not generated.
Humidity Alarm
The DS1923 has two Humidity Alarm Threshold regis-
ters (address 020Ah, 020Bh) to store values that deter-
mine whether humidity readings can generate an
alarm. Such an alarm is generated if the humidity data
read from the sensor qualifies for an alarm and the
alarm signaling is enabled. The bits EHLA and EHHA
that enable the humidity alarm are located in the
Humidity Sensor Control register. The corresponding
alarm flags HLF and HHF are found in the Alarm Status
register at address 0214h.
Bit 1: Enable Humidity High Alarm (EHHA). This bit
controls whether, during a mission, the humidity high
alarm flag (HHF) can be set, if a value from the humidi-
ty sensor is equal to or higher than the value in the
Humidity High Alarm Threshold register. If EHHA is 1,
humidity high alarms are enabled. If EHHA is 0, humidi-
ty high alarms are not generated.
Bit 0: Enable Humidity Low Alarm (EHLA). This bit
controls whether, during a mission, the humidity low
alarm flag (HLF) can be set, if a value from the humidity
sensor is equal to or lower than the value in the
Humidity Low Alarm Threshold register. If EHLA is 1,
humidity low alarms are enabled. If EHLA is 0, humidity
low alarms are not generated.
RTC Control
To minimize the power consumption of a DS1923, the
RTC oscillator should be turned off when the device is
not in use. The oscillator on/off bit is located in the RTC
Control register. This register also includes the EHSS
bit, which determines whether the sample rate is speci-
fied in seconds or minutes.
Bit 1: Enable High-Speed Sample (EHSS). This bit
controls the speed of the sample rate counter. When set
to logic 0, the sample rate is specified in minutes. When
set to logic 1, the sample rate is specified in seconds.
Temperature Sensor Control Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0210h 0 0 0 0 0 0 ETHA ETLA
RTC Control Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0212h 0 0 0 0 0 0 EHSS EOSC
Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.
Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be written to 1.
Humidity Sensor Control Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0211h 1 1 1 1 1 1 EHHA EHLA
Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 1 and cannot be written to 0.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 21www.maximintegrated.com
Bit 0: Enable Oscillator (EOSC). This bit controls the
crystal oscillator of the RTC. When set to logic 1, the
oscillator starts. When written to logic 0, the oscillator
stops and the device is in a low-power data-retention
mode. This bit must be 1 for normal operation. A
Forced Conversion or Start Mission command automati-
cally starts the RTC by changing the EOSC bit to
logic 1.
Mission Control
The DS1923 is set up for its operation by writing appro-
priate data to its special function registers, which are
located in the two register pages. The settings in the
Mission Control register determine whether temperature
and/or humidity is logged, which format (8 or 16 bits)
applies, and whether old data can be overwritten by
new data once the data-log memory is full. An addition-
al control bit can be set to tell the DS1923 to wait with
logging data until a temperature alarm is encountered.
Bit 5: Start Mission Upon Temperature Alarm
(SUTA). This bit specifies whether a mission begins
immediately (includes delayed start) or if a temperature
alarm is required to start the mission. If this bit is 1, the
device performs an 8-bit temperature conversion at the
selected sample rate and begins with data logging only
if an alarming temperature (high alarm or low alarm)
was found. The first logged temperature is when the
alarm occurred. However, the Mission Samples
Counter does not increment. The start upon tempera-
ture alarm function is only available if temperature log-
ging is enabled (ETL = 1).
Bit 4: Rollover Control (RO). This bit controls whether,
during a mission, the data-log memory is overwritten
with new data or whether data logging is stopped once
the data-log memory is full. Setting this bit to 1 enables
the rollover and data logging continues at the begin-
ning, overwriting previously collected data. If this bit is
0, the logging and conversions stop once the data-log
memory is full. However, the RTC continues to run and
the MIP bit remains set until the Stop Mission command
is performed.
Bit 3: Humidity Logging Format Selection (HLFS).
This bit specifies the format used to store humidity
readings in the data-log memory. If this bit is 0, the
data is stored in 8-bit format. If this bit is 1, the 16-bit
format is used (higher resolution). With 16-bit format,
the most significant byte is stored at the lower address.
Bit 2: Temperature Logging Format Selection
(TLFS). This bit specifies the format used to store tem-
perature readings in the data-log memory. If this bit is
0, the data is stored in 8-bit format. If this bit is 1, the
16-bit format is used (higher resolution). With 16-bit for-
mat, the most significant byte is stored at the lower
address.
Bit 1: Enable Humidity Logging (EHL). To set up the
DS1923 for a humidity-logging mission, this bit must be
set to logic 1. If temperature and humidity logging are
enabled, the recorded humidity values begin at
address 2000h (TLFS = HLFS) or 1A00h (TLFS = 0;
HLFS = 1) or 2400h (TLFS = 1; HLFS = 0). If only
humidity logging is enabled, the recorded values are
stored starting at address 1000h. Since humidity data
has little scientific value without knowing the tempera-
ture, typically both humidity and temperature logging
are enabled (i.e., ETL and EHL are set to 1).
Bit 0: Enable Temperature Logging (ETL). To set up
the device for a temperature-logging mission, this bit
must be set to logic 1. To successfully start a mission,
ETL or EHL must be 1. If temperature logging is
enabled, the recorded temperature values are always
stored starting at address 1000h.
Mission Control Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0213h 1 1 SUTA RO HLFS TLFS EHL ETL
Note: During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and cannot be written to 0.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 22www.maximintegrated.com
Alarm Status
The fastest way to determine whether a programmed
temperature or humidity threshold was exceeded during
a mission is through reading the Alarm Status register.
In a networked environment that contains multiple
DS1923 devices, the devices that encountered an alarm
can quickly be identified by means of the Conditional
Search ROM command (see the
1-Wire ROM Function
Commands
section). The humidity and temperature
alarm only occurs if enabled (see the
Temperature
Sensor Alarm
and
Humidity Alarm
sections). The BOR
alarm is always enabled.
Bit 7: Battery-On Reset Alarm (BOR). If this bit reads
1, the device has performed a power-on reset. This
indicates that the device has experienced a shock big
enough to interrupt the internal battery power supply.
The device can still appear functional, but it has lost its
factory calibration. Any data found in the data-log
memory should be disregarded.
Bit 3: Humidity High Alarm Flag (HHF). If this bit
reads 1, there was at least one humidity reading during
a mission revealing a value equal to or higher than the
value in the Humidity High Alarm register. A forced
conversion can affect the HHF bit.
Bit 2: Humidity Low Alarm Flag (HLF). If this bit reads
1, there was at least one humidity reading during a mis-
sion revealing a value equal to or lower than the value
in the Humidity Low Alarm register. A forced conversion
can affect the HLF bit.
Bit 1: Temperature High Alarm Flag (THF). If this bit
reads 1, there was at least one temperature conversion
during a mission revealing a temperature equal to or
higher than the value in the Temperature High Alarm
register. A forced conversion can affect the THF bit.
This bit can also be set with the initial alarm in the
SUTA = 1 mode.
Bit 0: Temperature Low Alarm Flag (TLF). If this bit
reads 1, there was at least one temperature conversion
during a mission revealing a temperature equal to or
lower than the value in the Temperature Low Alarm reg-
ister. A forced conversion can affect the TLF bit. This
bit can also be set with the initial alarm in the SUTA = 1
mode.
General Status
The information in the General Status register tells the
host computer whether a mission-related command
was executed successfully. Individual status bits indi-
cate whether the DS1923 is performing a mission, wait-
ing for a temperature alarm to trigger the logging of
data or whether the data from the latest mission has
been cleared.
Bit 4: Waiting for Temperature Alarm (WFTA). If this
bit reads 1, the mission start upon temperature alarm
was selected and the Start Mission command was suc-
cessfully executed, but the device has not yet experi-
enced the temperature alarm. This bit is cleared after a
temperature alarm event, but is not affected by the
Clear Memory command. Once set, WFTA remains set
if a mission is stopped before a temperature alarm
occurs. To clear WFTA manually before starting a new
mission, set the high temperature alarm (address
0209h) to -40°C and perform a forced conversion.
Bit 3: Memory Cleared (MEMCLR). If this bit reads 1,
the Mission Timestamp, Mission Samples Counter, and
all the alarm flags of the Alarm Status register have
been cleared in preparation of a new mission. Executing
the Clear Memory command clears these memory sec-
tions. The MEMCLR bit returns to 0 as soon as a new
mission is started by using the Start Mission command.
The memory must be cleared for a mission to start.
Bit 1: Mission in Progress (MIP). If this bit reads 1, the
device has been set up for a mission and this mission is
still in progress. The MIP bit returns from logic 1 to logic
0 when a mission is ended. See the
Start Mission [with
Password] [CCh]
and
Stop Mission [with Password]
[33h]
sections.
Alarm Status Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0214h BOR 1 1 1 HHF HLF THF TLF
General Status Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0215h 1 1 0 WFTA MEMCLR 0 MIP 0
Note: There is only read access to this register. Bits 4 to 6 have no function. They always read 1. All five alarm status bits are cleared
simultaneously when the Clear Memory command is invoked. See the
Memory and Control Function Commands
section for details.
Note: There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 23www.maximintegrated.com
Mission Samples Counter Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0220h Low Byte
0221h Center Byte
0222h High Byte
Mission Timestamp Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0219h 0 10 Seconds Single Seconds
021Ah 0 10 Minutes Single Minutes
021Bh 0 12/24
20 Hours
AM/PM 10 Hours Single Hours
021Ch 0 0 10 Date Single Date
021Dh CENT 0 0 10 Months Single Months
021Eh 10 Years Single Years
Mission Start Delay
The content of the Mission Start Delay Counter register
tells how many minutes must expire from the time a mis-
sion was started until the first measurement of the mis-
sion takes place (SUTA = 0) or until the device starts
testing the temperature for a temperature alarm (SUTA =
1). The Mission Start Delay register is stored as an
unsigned 24-bit integer number. The maximum delay is
16,777,215min, equivalent to 11,650 days or roughly
31yr. If the start delay is nonzero and the SUTA bit is set
to 1, first the delay must expire before the device starts
testing for temperature alarms to begin logging data.
For a typical mission, the Mission Start Delay is 0. If a
mission is too long for a single DS1923 to store all read-
ings at the selected sample rate, one can use several
devices and set the Mission Start Delay for the second
device to start recording as soon as the memory of the
first device is full, and so on. The RO bit in the Mission
Control register (address 0213h) must be set to 0 to
prevent overwriting of collected data once the data-log
memory is full.
Mission Timestamp
The Mission Timestamp register indicates the date and time
of the first temperature and humidity sample of the mission.
There is only read access to the Mission Timestamp register.
Mission Progress Indicator
Depending on settings in the Mission Control register
(address 0213h), the DS1923 logs temperature and/or
humidity in 8-bit or 16-bit format. The description of the
ETL and EHL bit explains where the device stores data
in its data-log memory. The Mission Samples Counter
register together with the starting address and the log-
ging format (8 or 16 bits) provide the information to iden-
tify valid blocks of data that have been gathered during
the current (MIP = 1) or latest mission (MIP = 0). See the
Data-Log Memory Usage
section for an illustration. Note
that when SUTA = 1, the Mission Samples Counter does
not increment when the first sample is logged.
The number read from the Mission Samples Counter indi-
cates how often the DS1923 woke up during a mission to
measure temperature and/or humidity. The number for-
mat is 24-bit unsigned integer. The Mission Samples
Counter is reset through the Clear Memory command.
Note: There is only read access to this register. Note that when both the internal temperature and humidity logging are enabled, the
two log readings are counted as one event in the Mission Samples Counter and Device Samples Counter.
Note: There is only read access to this register.
Mission Start Delay Counter Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0216h Delay Low Byte
0217h Delay Center Byte
0218h Delay High Byte
Note: During a mission, there is only read access to this register.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 24www.maximintegrated.com
Other Indicators
The Device Samples Counter register is similar to the
Mission Samples Counter register. During a mission this
counter increments whenever the DS1923 wakes up to
measure and log data and when the device is testing
for a temperature alarm in Start Mission Upon
Temperature Alarm mode. Between missions, the
counter increments whenever the Forced Conversion
command is executed. This way the Device Samples
Counter register functions like a gas gauge for the bat-
tery that powers the iButton device.
The Device Samples Counter register is reset to zero
when the iButton device is assembled. The number for-
mat is 24-bit unsigned integer. The maximum number
that can be represented in this format is 16,777,215.
Due to the calibration and tests at the factory, new
devices can have a count value of up to 35,000. The
typical value is well below 10,000.
The code in the Device Configuration register allows the
master to distinguish between the DS2422 chip and dif-
ferent versions of the DS1922 devices. The
Device
Configuration Register Bitmap
table shows the codes
assigned to the various devices.
Security by Password
The DS1923 is designed to use two passwords that
control read access and full access. Reading from or
writing to the scratchpad as well as the Forced
Conversion command does not require a password.
The password must be transmitted immediately after
the command code of the memory or control function. If
password checking is enabled, the password transmit-
ted is compared to the passwords stored in the device.
The data pattern stored in the Password Control regis-
ter determines whether password checking is enabled.
To enable password checking, the EPW bits need to
form a binary pattern of 10101010 (AAh). The default
pattern of EPW is different from AAh. If the EPW pattern
is different from AAh, any pattern is accepted as long
as it has a length of exactly 64 bits. Once enabled,
changing the passwords and disabling password
checking requires the knowledge of the current full-
access password.
Device Samples Counter Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0223h Low Byte
0224h Center Byte
0225h High Byte
Password Control Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0227h EPW
Device Configuration Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 PART
0 0 0 0 0 0 0 0 DS2422
0 0 1 0 0 0 0 0 DS1923
0 1 0 0 0 0 0 0 DS1922L
0 1 1 0 0 0 0 0 DS1922T
0226h
1 0 0 0 0 0 0 0 DS1922E
Note: There is only read access to this register.
Note: There is only read access to this register.
Note: During a mission, there is only read access to this register.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 25www.maximintegrated.com
Before enabling password checking, passwords for
read-only access as well as for full access
(read/write/control) must be written to the password
registers. Setting up a password or enabling/dis-
abling the password checking is done in the same
way as writing data to a memory location; only the
address is different. Since they are located in the
same memory page, both passwords can be rede-
fined at the same time.
The Read Access Password must be transmitted exact-
ly in the sequence RP0, RP1…RP62, RP63. This pass-
word only applies to the Read Memory with CRC
command. The DS1923 delivers the requested data
only if the password transmitted by the master was cor-
rect or if password checking is not enabled.
The Full Access Password must be transmitted exactly
in the sequence FP0, FP1…FP62, FP63. It affects the
commands Read Memory with CRC, Copy Scratchpad,
Clear Memory, Start Mission, and Stop Mission. The
DS1923 executes the command only if the password
transmitted by the master was correct or if password
checking is not enabled.
Due to the special behavior of the write-access logic,
the Password Control register and both passwords
must be written at the same time. When setting up new
passwords, always verify (read back) the scratchpad
before sending the Copy Scratchpad command. After a
new password is successfully copied from the scratch-
pad to its memory location, erase the scratchpad by fill-
ing it with new data (Write Scratchpad command).
Otherwise, a copy of the passwords remains in the
scratchpad for public read access.
Read-Access Password Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0228h RP7 RP6 RP5 RP4 RP3 RP2 RP1 RP0
0229h RP15 RP14 RP13 RP12 RP11 RP10 RP9 RP8
… …
022Eh RP55 RP54 RP53 RP52 RP51 RP50 RP49 RP48
022Fh RP63 RP62 RP61 RP60 RP59 RP58 RP57 RP56
Full-Access Password Register Bitmap
ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
0230h FP7 FP6 FP5 FP4 FP3 FP2 FP1 FP0
0231h FP15 FP14 FP13 FP12 FP11 FP10 FP9 FP8
… …
0236h FP55 FP54 FP53 FP52 FP51 FP50 FP49 FP48
0237h FP63 FP62 FP61 FP60 FP59 FP58 FP57 FP56
Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot be
changed while a mission is in progress.
Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot be
changed while a mission is in progress.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 26www.maximintegrated.com
Data-Log Memory Usage
Once set up for a mission, the DS1923 logs the temper-
ature and/or humidity measurements at equidistant time
points entry after entry in its data-log memory. The
data-log memory can store 8192 entries in 8-bit format
or 4096 entries in 16-bit format (Figure 7a). If tempera-
ture as well as humidity are logged, both in the same
format, the memory is split into two equal sections that
can store 4096 8-bit entries or 2048 16-bit entries
(Figure 7b). If the device is set up to log data in differ-
ent formats, e. g., temperature in 8-bit and humidity in
16-bit format, the memory is split into blocks of different
size, accommodating 2560 entries for either data
source (Figure 7c). In this case, the upper 256 bytes
are not used. In 16-bit format, the higher 8 bits of an
entry are stored at the lower address. Knowing the
starting time point (Mission Timestamp) and the interval
between temperature measurements, one can recon-
struct the time and date of each measurement.
There are two alternatives to the way the DS1923
behaves after the data-log memory is filled with data.
The user can program the device to either stop any fur-
ther recording (disable rollover) or overwrite the previ-
ously recorded data (enable rollover), one entry at a
time, starting again at the beginning of the respective
memory section. The contents of the Mission Samples
Counter in conjunction with the sample rate and the
Mission Timestamp allow reconstructing the time
points of all values stored in the data-log memory. This
gives the exact history over time for the most recent
measurements taken. Earlier measurements cannot be
reconstructed.
Missioning
The typical task of the DS1923 is recording temperature
and/or humidity. Before the device can perform this
function, it needs to be set up properly. This procedure
is called missioning.
First, the DS1923 must have its RTC set to a valid time
and date. This reference time can be the local time, or,
when used inside of a mobile unit, UTC (also called
GMT, Greenwich Mean Time), or any other time stan-
dard that was agreed upon. The RTC oscillator must be
running (EOSC = 1). The memory assigned to store the
Mission Timestamp, Mission Samples Counter, and
alarm flags must be cleared using the Clear Memory
command. To enable the device for a mission, at least
one of the enable logging bits (ETL, EHL) must be set
to 1. These are general settings that must be made in
any case, regardless of the type of object to be moni-
tored and the duration of the mission.
If alarm signaling is desired, the temperature alarm
and/or humidity alarm low and high thresholds must be
defined. See the
Temperature Conversion
section for
information on how to convert a temperature value into
the binary code to be written to the threshold registers.
See the
Humidity Conversion
section for information on
determining the thresholds for the humidity alarm. In
addition, the temperature alarm and/or humidity alarm
must be enabled for the low and/or high threshold. This
makes the device respond to a Conditional Search
ROM command (see the
1-Wire ROM Function
Commands
section), provided that an alarming condi-
tion has been encountered.
The setting of the RO bit (rollover enable) and sample
rate depends on the duration of the mission and the
monitoring requirements. If the most recently logged
data is important, the rollover should be enabled (RO =
1). Otherwise one should estimate the duration of the
mission in minutes and divide the number by 8192 (sin-
gle channel 8-bit format) or 4096 (single channel 16-bit
format, two channels 8-bit format) or 2048 (two channels
16-bit format) or 2560 (two channels, one 8-bit and one
16-bit format) to calculate the value of the sample rate
(number of minutes between conversions). If the esti-
mated duration of a mission is 10 days (= 14400min), for
example, then the 8192-byte capacity of the data-log
memory would be sufficient to store a new 8-bit value
every 1.8min (110s). If the data-log memory of the
DS1923 is not large enough to store all readings, one
can use several devices and set the Mission Start Delay
to values that make the second device start logging as
soon as the memory of the first device is full, and so on.
The RO-bit needs to be set to 0 to disable rollover that
would otherwise overwrite the logged data.
After the RO bit and the Mission Start Delay are set, the
sample rate must be written to the Sample Rate regis-
ter. The sample rate can be any value from 1 to 16,383,
coded as an unsigned 14-bit binary number. The
fastest sample rate is one sample per second (EHSS =
1, sample rate = 0001h) and the slowest is one sample
every 273.05hr (EHSS = 0, sample rate = 3FFFh). To
get one sample every 6min, for example, the sample
rate value must be set to 6 (EHSS = 0) or 360 decimal
(equivalent to 0168h at EHSS = 1).
If there is a risk of unauthorized access to the DS1923
or manipulation of data, one should define passwords
for read access and full access. Before the passwords
become effective, their use must be enabled. See the
Security by Password
section for more details.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 27www.maximintegrated.com
8192
8-BIT ENTRIES
TEMPERATURE
OR
HUMIDITY DATA
ETL = 1; EHL = 0 OR ETL = 0; EHL = 1
TLFS = HLFS = 0
1000h
2FFFh
4096
16-BIT ENTRIES
TEMPERATURE
OR
HUMIDITY DATA
WITH 16-BIT FORMAT, THE MOST SIGNIFICANT
BYTE IS STORED AT THE LOWER ADDRESS.
ETL = 1; EHL = 0 OR ETL = 0; EHL = 1
TLFS = HLFS = 1
1000h
2FFFh
Figure 7a. 1-Channel Logging
TEMPERATURE
4096
8-BIT ENTRIES
ETL = EHL = 1
TLFS = HLFS = 0
1000h
1FFFh
HUMIDITY DATA
4096
8-BIT ENTRIES
2000h
2FFFh
TEMPERATURE
2048
16-BIT ENTRIES
WITH 16-BIT FORMAT, THE MOST SIGNIFICANT
BYTE IS STORED AT THE LOWER ADDRESS.
ETL = EHL = 1
TLFS = HLFS = 1
1000h
1FFFh
HUMIDITY DATA
2048
16-BIT ENTRIES
2000h
2FFFh
Figure 7b. 2-Channel Logging, Equal Resolution
TEMPERATURE
2560
8-BIT ENTRIES
ETL = EHL = 1
TLFS = 0; HLFS = 1
1000h
19FFh
HUMIDITY DATA
2560
16-BIT ENTRIES
1A00h
2DFFh
TEMPERATURE
2560
16-BIT ENTRIES
WITH 16-BIT FORMAT, THE MOST SIGNIFICANT
BYTE IS STORED AT THE LOWER ADDRESS.
ETL = EHL = 1
TLFS = 1; HLFS = 0
1000h
23FFh
HUMIDITY DATA
2560
8-BIT ENTRIES
2400h
2DFFh
(NOT USED) (NOT USED)
2E00h
2FFFh
2E00h
2FFFh
Figure 7c. 2-Channel Logging, Different Resolution
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 28www.maximintegrated.com
The last step to begin a mission is to issue the Start
Mission command. As soon as it has received this com-
mand, the DS1923 sets the MIP flag and clears the
MEMCLR flag. With the immediate/delayed start mode
(SUTA = 0), after as many minutes as specified by the
Mission Start Delay are over, the device wakes up,
copies the current date and time to the Mission
Timestamp register, and logs the first entry of the mis-
sion. This increments both the Mission Samples
Counter and Device Samples Counter. All subsequent
log entries are made as specified by the value in the
Sample Rate register and the EHSS bit.
If the start upon temperature alarm mode is chosen
(SUTA = 1) and temperature logging is enabled (ETL =
1), the DS1923 first waits until the start delay is over.
Then the device wakes up in intervals as specified by
the sample rate and EHSS bit and measures the tem-
perature. This increments the Device Samples Counter
register only. The first sample of the mission is logged
when the temperature alarm occurred. However, the
Mission Samples Counter does not increment. One
sample period later the Mission Timestamp register is
set. From then on, both the Mission Samples Counter
and Device Samples Counter registers increment at the
same time. All subsequent log entries are made as
specified by the value in the Sample Rate register and
the EHSS bit.
The general-purpose memory operates independently of
the other memory sections and is not write protected
during a mission. All the DS1923’s memory can be read
at any time, e.g., to watch the progress of a mission.
Attempts to read the passwords read 00h bytes instead
of the data that is stored in the password registers.
Memory Access
Address Registers and Transfer Status
Because of the serial data transfer, the DS1923
employs three address registers called TA1, TA2, and
E/S (Figure 8). Registers TA1 and TA2 must be loaded
with the target address to which the data is written or
from which data is sent to the master upon a read com-
mand. Register E/S acts like a byte counter and trans-
fer status register. It is used to verify data integrity with
write commands. Therefore, the master only has read
access to this register. The lower 5 bits of the E/S regis-
ter indicate the address of the last byte that has been
written to the scratchpad. This address is called ending
offset. The DS1923 requires that the ending offset is
always 1Fh for a Copy Scratchpad to function. Bit 5
of the E/S register, called PF or partial byte flag, is set if
the number of data bits sent by the master is not an
integer multiple of 8. Bit 6 is always a 0. Note that the
lowest 5 bits of the target address also determine the
address within the scratchpad, where intermediate
storage of data begins. This address is called byte off-
set. If the target address for a Write Scratchpad com-
mand is 13Ch, for example, the scratchpad stores
incoming data beginning at the byte offset 1Ch and is
full after only 4 bytes. The corresponding ending offset
in this example is 1Fh. For best economy of speed and
BIT NUMBER 7 6 5 4 3 2 1 0
TARGET ADDRESS (TA1) T7 T6 T5 T4 T3 T2 T1 T0
TARGET ADDRESS (TA2) T15 T14 T13 T12 T11 T10 T9 T8
ENDING ADDRESS WITH
DATA STATUS (E/S)
(READ ONLY)
AA 0 PF E4 E3 E2 E1 E0
Figure 8. Address Registers
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 29www.maximintegrated.com
efficiency, the target address for writing should point to
the beginning of a page, i.e., the byte offset is 0. Thus,
the full 32-byte capacity of the scratchpad is available,
resulting also in the ending offset of 1Fh. The ending
offset together with the PF flag are a means to support
the master checking the data integrity after a Write
Scratchpad command. The highest valued bit of the
E/S register, called authorization accepted (AA), indi-
cates that a valid Copy Scratchpad command for the
scratchpad has been received and executed. Writing
data to the scratchpad clears this flag.
Writing with Verification
To write data to the DS1923, the scratchpad must be
used as intermediate storage. First, the master issues
the Write Scratchpad command to specify the desired
target address, followed by the data to be written to the
scratchpad. In the next step, the master sends the
Read Scratchpad command to read the scratchpad
and to verify data integrity. As preamble to the scratch-
pad data, the DS1923 sends the requested target
address TA1 and TA2 and the contents of the E/S
Register. If the PF flag is set, data did not arrive cor-
rectly in the scratchpad. The master does not need to
continue reading; it can start a new trial to write data to
the scratchpad. Similarly, a set AA flag indicates that
the Write Scratchpad command was not recognized by
the device. If everything went correctly, both flags are
cleared and the ending offset indicates the address of
the last byte written to the scratchpad. Now the master
can continue verifying every data bit. After the master
has verified the data, it must send the Copy Scratchpad
command. This command must be followed exactly by
the data of the three address registers TA1, TA2, and
E/S, as the master has read them verifying the scratch-
pad. As soon as the DS1923 has received these bytes,
it copies the data to the requested location beginning
at the target address.
Memory and Control
Function Commands
Figure 9 shows the protocols necessary for accessing
the memory and the special function registers of the
DS1923. An example on how to use these and other
functions to set up the DS1923 for a mission is included
in the
Mission Example: Prepare and Start a New
Mission
section. The communication between the mas-
ter and the DS1923 takes place either at standard
speed (default, OD = 0) or at overdrive speed (OD =
1). If not explicitly set into the overdrive mode, the
DS1923 assumes standard speed. Internal memory
access during a mission has priority over external
access through the 1-Wire interface. This affects sever-
al commands in this section. See the
Memory Access
Conflicts
section for details and solutions.
Write Scratchpad [0Fh]
After issuing the Write Scratchpad command, the mas-
ter must first provide the 2-byte target address, fol-
lowed by the data to be written to the scratchpad. The
data is written to the scratchpad starting at the byte off-
set T[4:0]. The master must send as many bytes as are
needed to reach the ending offset of 1Fh. If a data byte
is incomplete, its content is ignored and the partial byte
flag PF is set.
When executing the Write Scratchpad command, the
CRC generator inside the DS1923 calculates a CRC of
the entire data stream, starting at the command code
and ending at the last data byte sent by the master
(Figure 15). This CRC is generated using the CRC-16
polynomial by first clearing the CRC generator and then
shifting in the command code (0Fh) of the Write
Scratchpad command, the target addresses TA1 and
TA2 as supplied by the master, and all the data bytes.
If the ending offset is 11111b, the master can send 16
read time slots and receive the inverted CRC-16 gener-
ated by the DS1923.
Note that both register pages are write protected dur-
ing a mission. Although the Write Scratchpad command
works normally at any time, the subsequent copy
scratchpad to a register page fails during a mission.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 30www.maximintegrated.com
Read Scratchpad [AAh]
This command is used to verify scratchpad data and
target address. After issuing the Read Scratchpad
command, the master begins reading. The first 2 bytes
are the target address. The next byte is the ending off-
set/data status byte (E/S) followed by the scratchpad
data beginning at the byte offset T[4:0], as shown in
Figure 8. The master can continue reading data until
the end of the scratchpad after which it receives an
inverted CRC-16 of the command code, target
addresses TA1 and TA2, the E/S byte, and the scratch-
pad data starting at the target address. After the CRC
is read, the bus master reads logic 1s from the DS1923
until a reset pulse is issued.
Copy Scratchpad [with Password] [99h]
This command is used to copy data from the scratch-
pad to the writable memory sections. After issuing the
Copy Scratchpad command, the master must provide a
3-byte authorization pattern, which can be obtained by
reading the scratchpad for verification. This pattern
must exactly match the data contained in the three
address registers (TA1, TA2, E/S, in that order). Next,
the master must transmit the 64-bit full access pass-
word. If passwords are enabled and the transmitted
password is different from the stored full access pass-
word, the Copy Scratchpad command fails. The device
stops communicating and waits for a reset pulse. If the
password was correct or if passwords were not
enabled, the device tests the 3-byte authorization code.
If the authorization code pattern matches, the AA flag is
set and the copy begins. A pattern of alternating 1s and
0s is transmitted after the data has been copied until
the master issues a reset pulse. While the copy is in
progress, any attempt to reset the part is ignored. Copy
typically takes 2μs per byte.
The data to be copied is determined by the three
address registers. The scratchpad data from the begin-
ning offset through the ending offset are copied, start-
ing at the target address. The AA flag remains at logic
1 until it is cleared by the next Write Scratchpad com-
mand. With suitable password, the copy scratchpad
always functions for the 16 pages of data memory and
the 2 pages of calibration memory. While a mission is in
progress, write attempts to the register pages are not
successful. The AA bit remaining at 0 indicates this.
Read Memory with [Password
and] CRC [69h]
The Read Memory with CRC command is the general
function to read from the device. This command gener-
ates and transmits a 16-bit CRC following the last data
byte of a memory page.
After having sent the command code of the Read
Memory with CRC command, the bus master sends a
2-byte address that indicates a starting byte location.
Next, the master must transmit one of the 64-bit pass-
words. If passwords are enabled and the transmitted
password does not match one of the stored passwords,
the Read Memory with CRC command fails. The device
stops communicating and waits for a reset pulse. If the
password was correct or if passwords were not
enabled, the master reads data from the DS1923
beginning from the starting address and continuing
until the end of a 32-byte page is reached. At that point
the bus master sends 16 additional read-data time slots
and receives the inverted 16-bit CRC. With subsequent
read-data time slots the master receives data starting at
the beginning of the next memory page followed again
by the CRC for that page. This sequence continues
until the bus master resets the device. When trying to
read the passwords or memory areas that are marked
as “reserved,” the DS1923 transmits 00h or FFh bytes,
respectively. The CRC at the end of a 32-byte memory
page is based on the data as it was transmitted.
With the initial pass through the Read Memory with
CRC flow, the 16-bit CRC value is the result of shifting
the command byte into the cleared CRC generator fol-
lowed by the 2 address bytes and the contents of the
data memory. Subsequent passes through the Read
Memory with CRC flow generate a 16-bit CRC that is
the result of clearing the CRC generator and then shift-
ing in the contents of the data memory page. After the
16-bit CRC of the last page is read, the bus master
receives logic 1s from the DS1923 until a reset pulse is
issued. The Read Memory with CRC command
sequence can be ended at any point by issuing a reset
pulse.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 31www.maximintegrated.com
MASTER Tx MEMORY OR
CONTROL FUNCTION COMMAND
MASTER Tx
TA1 [T7:T0]
MASTER Tx DATA BYTE
TO SCRATCHPAD OFFSET
DS1923
INCREMENTS
SCRATCHPAD
OFFSET
DS1923 SETS
SCRATCHPAD OFFSET = [T4:T0]
AND CLEARS (PF, AA)
0Fh
WRITE SCRATCHPAD? N
Y
Y
N
Y
N
N
Y
N
MASTER Tx RESET?
SCRATCHPAD
OFFSET = 11111b?
MASTER Tx RESET?
MASTER Tx RESET?
MASTER Tx
TA2 [T15:T8]
DS1923 SETS [E4:E0] =
SCRATCHPAD OFFSET
N
FROM ROM FUNCTIONS
FLOWCHART (FIGURE 11)
TO ROM FUNCTIONS
FLOWCHART (FIGURE 11)
Y
Y
TO FIGURE 9b
FROM FIGURE 9b
MASTER Rx CRC-16 OF
COMMAND, ADDRESS DATA
MASTER Rx "1"s
PARTIAL
BYTE WRITTEN?
PF = 1
AA = 1
MASTER Rx
TA1 [T7:T0]
DS1923 SETS
SCRATCHPAD OFFSET = [T4:T0]
DS1923
INCREMENTS
SCRATCHPAD
OFFSET
MASTER Rx ENDING OFFSET
WITH DATA STATUS
(E/S)
AAh
READ SCRATCHPAD? N
Y
Y
N
Y
N
Y
N
MASTER Tx RESET?
SCRATCHPAD
OFFSET = 11111b?
MASTER Tx RESET?
MASTER Rx
TA2 [T15:T8]
MASTER Rx DATA BYTE FROM
SCRATCHPAD OFFSET
MASTER Rx CRC-16 OF
COMMAND, ADDRESS DATA,
E/S BYTE, AND DATA STARTING
AT THE TARGET ADDRESS
MASTER Rx "1"s
99h
COPY SCRATCHPAD
[WITH PW]
N
Y
Y
N
N
MASTER Tx RESET?
MASTER Tx RESET?
COPYING
FINISHED
MASTER Tx
E/S BYTE
MASTER Tx
TA1 [T7:T0], TA2 [T15:T8]
AUTHORIZATION
CODE
MASTER Tx
64 BITS [PASSWORD]
DS1923 COPIES SCRATCHPAD
DATA TO MEMORY
N
Y
AUTHORIZATION
CODE MATCH?
N
Y
N
Y
Y
NMASTER Tx RESET?
Y
PASSWORD
ACCEPTED?
DS1923 Tx "0"
DS1923 Tx "1"
MASTER Rx "1"s MASTER Rx "1"s
Figure 9a. Memory/Control Function Flowchart
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 32www.maximintegrated.com
FROM FIGURE 9a
TO FIGURE 9a
TO FIGURE 9c
FROM FIGURE 9c
69h
READ MEMORY [WITH
PW] AND CRC
N
N
Y
Y
N
N
END OF MEMORY?
MASTER Tx RESET?
CRC OK?
MASTER Tx
64 BITS [PASSWORD]
MASTER Tx
TA1 [T7:T0], TA2 [T15:T8]
DS1923 SETS
MEMORY ADDRESS = [T15:T0]
MASTER Rx DATA BYTE FROM
MEMORY ADDRESS
Y
N
N
N
END OF PAGE?
DECISION MADE
BY MASTER
DECISION MADE
BY DS1923
Y
N
Y
Y
MASTER Tx RESET?
Y
PASSWORD
ACCEPTED?
MASTER Tx RESET
MASTER Rx "1"s
MASTER Rx CRC-16 OF
COMMAND, ADDRESS, DATA
(1ST PASS); CRC-16 OF DATA
(SUBSEQUENT PASSES)
DS1923
INCREMENTS
ADDRESS
COUNTER
N
Y
MASTER Tx
FFh DUMMY BYTE
MASTER Tx
64 BITS [PASSWORD]
DS1923 SETS
MEMCLR = 1
Y
MISSION IN
PROGRESS?
N
N
Y
MASTER Tx RESET?
Y
PASSWORD
ACCEPTED?
DS1923 CLEARS
MISSION TIMESTAMP,
MISSION SAMPLES COUNTER,
ALARM FLAGS
96h
CLEAR MEMORY
[WITH PW]
N
N
Y
MASTER Tx
FFh DUMMY BYTE
DS1923 COPIES RESULT TO
ADDRESS 020C/Dh
DS1923 PERFORMS A
TEMPERATURE CONVERSION
DS1923 PERFORMS A
HUMIDITY CONVERSION
DS1923 COPIES RESULT TO
ADDRESS 020E/Fh
Y
MISSION IN
PROGRESS?
N
MASTER Tx RESET?
Y
55h
FORCED CONVERSION?
Figure 9b. Memory/Control Function Flowchart (continued)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 33www.maximintegrated.com
MISSION START
DELAY PROCESS
FROM FIGURE 9b
TO FIGURE 9b
Y
START DELAY
COUNTER = 0?
N
N
SUTA = 1?
Y
N
TEMPERATURE
ALARM?
Y
MIP = 0?
N
N
N
Y
MASTER Tx
FFh DUMMY BYTE
MASTER Tx
64 BITS [PASSWORD]
DS1923 WAITS FOR 1 MINUTE
DS1923 SETS WFTA = 1
DS1923 SETS WFTA = 0
AND LOGS FIRST SAMPLE
THE MISSION
SAMPLES COUNTER
DOES NOT
INCREMENT
DS1923 DECREMENTS
START DELAY COUNTER
DS1923 WAITS ONE
SAMPLE PERIOD
DS1923 PERFORMS 8-BIT
TEMPERATURE CONVERSION
DS1923 WAITS ONE
SAMPLE PERIOD
IF SUTA = 1,
THIS IS THE
SECOND SAMPLE.
MISSION IN
PROGRESS?
N
Y
MASTER Tx RESET?
Y
PASSWORD
ACCEPTED?
N
Y
Y
MEMCLR = 1?
Y
N
DS1923 SETS
MIP = 1,
MEMCLR = 0
DS1923 COPIES RTC DATA TO
MISSION TIMESTAMP REGISTER
DS1923 STARTS LOGGING
TAKING FIRST SAMPLE
DS1923 INITIATES MISSION
START DELAY PROCESS
CCh
START MISSION
[WITH PW]
N
Y
MASTER Tx
FFh DUMMY BYTE
MASTER Tx
64 BITS [PASSWORD]
MISSION IN
PROGRESS?
Y
Y
MASTER Tx RESET?
Y
PASSWORD
ACCEPTED?
DS1923 SETS
MIP = 0,
WFTA = 0
33h
STOP MISSION
[WITH PW]
N
N
N
END OF PROCESS
Figure 9c. Memory/Control Function Flowchart (continued)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 34www.maximintegrated.com
Clear Memory [with Password] [96h]
The Clear Memory with Password command is used to
prepare the device for another mission. This command
is only executed if no mission is in progress. After the
command code, the master must transmit the 64-bit
full-access password followed by an FFh dummy byte.
If passwords are enabled and the transmitted pass-
word is different from the stored full access password
or a mission is in progress, the Clear Memory com-
mand fails. The device stops communicating and waits
for a reset pulse. If the password was correct or if pass-
words were not enabled, the device clears the Mission
Timestamp register, Mission Samples Counter register,
and all alarm flags of the Alarm Status register. After
these cells are cleared, the MEMCLR bit of the General
Status register reads 1 to indicate the successful exe-
cution of the Clear Memory with Password command.
Clearing of the data-log memory is not necessary
because the Mission Samples Counter indicates how
many entries in the data-log memory are valid.
Forced Conversion [55h]
The Forced Conversion command can be used to mea-
sure the temperature and humidity without starting a
mission. After the command code, the master must
send one FFh byte to get the conversion started. The
conversion result is found as a 16-bit value in the Latest
Temperature Conversion Result and Latest Humidity
Conversion Result registers. This command is only exe-
cuted if no mission is in progress (MIP = 0). It cannot
be interrupted and takes maximum 666ms to complete.
During this time memory access through the 1-Wire
interface is blocked. The device behaves the same way
as during a mission when the sampling interferes with a
memory/control function command. See the
Memory
Access Conflicts
section for details.
Start Mission [with Password] [CCh]
The DS1923 uses a control function command to start a
mission. A new mission can only be started if the previ-
ous mission has been ended and the memory has been
cleared. After the command code, the master must
transmit the 64-bit full access password followed by an
FFh dummy byte. If passwords are enabled and the
transmitted password is different from the stored full-
access password or a mission is in progress, the Start
Mission command fails. The device stops communicat-
ing and waits for a reset pulse. If the password was
correct or if passwords were not enabled, the device
starts a mission. If SUTA = 0, the sampling begins as
soon as the Mission Start Delay is over. If SUTA = 1, the
first sample is written to the data-log memory at the
time the temperature alarm occurred. However, the
Mission Samples Counter does not increment. One
sample period later, the Mission Timestamp register is
set and the regular sampling and logging begins. While
the device is waiting for a temperature alarm to occur,
the WFTA flag in the General Status register reads 1.
During a mission there is only read access to the regis-
ter pages.
Stop Mission [with Password] [33h]
The DS1923 uses a control function command to stop a
mission. Only a mission that is in progress can be
stopped. After the command code, the master must
transmit the 64-bit full access password followed by a
FFh dummy byte. If passwords are enabled and the
transmitted password is different from the stored full-
access password or a mission is not in progress, the
Stop Mission command fails. The device stops commu-
nicating and waits for a reset pulse. If the password
was correct or if passwords were not enabled, the
device clears the MIP bit in the General Status register
and restores write access to the register pages. The
WFTA bit is not cleared. See the description of the gen-
eral status register for a method to clear the WFTA bit.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 35www.maximintegrated.com
Memory Access Conflicts
While a mission is in progress or while the device is
waiting for a temperature alarm to start a mission, peri-
odically a temperature and/or humidity sample is taken
and logged. This “internal activity” has priority over
1-Wire communication. As a consequence, device-spe-
cific commands (excluding ROM function commands
and 1-Wire reset) do not perform properly when internal
and “external” activities interfere with each other. Not
affected are the commands Start Mission, Forced
Conversion, and Clear Memory, because they are not
applicable while a mission is in progress or while the
device is waiting for a temperature alarm. Table 5
explains how the remaining five commands are affect-
ed by internal activity, how to detect this interference,
and how to work around it.
The interference is more likely to be seen with a high-
sample rate (one sample every second) and with high-
resolution logging, which can last up to 666ms when
both temperature and humidity are recorded. With
lower sample rates, interference may hardly be visible
at all. In any case, when writing driver software it is
important to know about the possibility of interference
and to take measures to work around it.
Table 5. Memory Access Conflicts and Solutions
COMMAND INDICATION OF INTERFERENCE SOLUTION
Write Scratchpad The CRC-16 at the end of the command flow reads
FFFFh.
Wait 0.5s, 1-Wire reset, address the device, repeat
Write Scratchpad with the same data, and check the
validity of the CRC-16 at the end of the command
flow. Alternatively, use Read Scratchpad to verify
data integrity.
Read Scratchpad
The data read changes to FFh bytes or all bytes
received are FFh, including the CRC at the end of
the command flow.
Wait 0.5s, 1-Wire reset, address the device, repeat
Read Scratchpad, and check the validity of the
CRC-16 at the end of the command flow.
Copy Scratchpad
The device behaves as if the authorization code or
password was not valid or as if the copy function
would not end.
Wait 0.5s, 1-Wire reset, address the device, issue
Read Scratchpad, and check the AA bit of the E/S
byte. If the AA bit is set, Copy Scratchpad was
successful.
Read Memory with
CRC
The data read changes to all FFh bytes or all bytes
received are FFh, including the CRC at the end of
the command flow, despite a valid password.
Wait 0.5s, 1-Wire reset, address the device, repeat
Read Memory with CRC, and check the validity of
the CRC-16 at the end of the memory page.
Stop Mission The General Status register at address 0215h reads
FFh or the MIP bit is 1 while bits 0, 2, and 5 are 0.
Wait 0.5s, 1-Wire reset, address the device, and
repeat Stop Mission. Perform a 1-Wire reset, address
the device, read the General Status register at
address 0215h, and check the MIP bit. If the MIP bit
is 0, Stop Mission was successful.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 36www.maximintegrated.com
1-Wire Bus System
The 1-Wire bus is a system that has a single bus mas-
ter and one or more slaves. In all instances the DS1923
is a slave device. The bus master is typically a micro-
controller. The discussion of this bus system is broken
down into three topics: hardware configuration, trans-
action sequence, and 1-Wire signaling (signal types
and timing). The 1-Wire protocol defines bus transac-
tions in terms of the bus state during specific time slots
that are initiated on the falling edge of sync pulses from
the bus master.
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is
important that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device
attached to the 1-Wire bus must have open-drain or
three-state outputs. The 1-Wire port of the DS1923 is
open drain with an internal circuit equivalent to that
shown in Figure 10.
A multidrop bus consists of a 1-Wire bus with multiple
slaves attached. At standard speed the 1-Wire bus has
a maximum data rate of 16.3kbps. The speed can be
boosted to 142kbps by activating the overdrive mode.
The DS1923 is not guaranteed to be fully compliant to
the iButton device standard. Its maximum data rate in
standard speed is 15.4kbps and 125kbps in overdrive
speed. The value of the pullup resistor primarily
depends on the network size and load conditions. The
DS1923 requires a pullup resistor of maximum 2.2kΩat
any speed.
The idle state for the 1-Wire bus is high. If for any rea-
son a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is to
resume. If this does not occur and the bus is left low for
more than 16μs (overdrive speed) or more than 120μs
(standard speed), one or more devices on the bus may
be reset. Note that the DS1923 does not quite meet the
full 16μs maximum low time of the normal 1-Wire bus
overdrive timing. With the DS1923 the bus must be left
low for no longer than 12μs at overdrive to ensure that
no DS1923 on the 1-Wire bus performs a reset. The
DS1923 communicates properly when used in conjunc-
tion with a DS2480B or DS2490 1-Wire driver and
adapters that are based on these driver chips.
Transaction Sequence
The protocol for accessing the DS1923 through the
1-Wire port is as follows:
• Initialization
• ROM Function Command
• Memory/Control Function Command
• Transaction/Data
Rx
RPUP
IL
VPUP
BUS MASTER
OPEN-DRAIN
PORT PIN 100Ω MOSFET
Tx
Rx
Tx
DATA
DS1923 1-Wire PORT
Rx = RECEIVE
Tx = TRANSMIT
Figure 10. Hardware Configuration
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 37www.maximintegrated.com
Initialization
All transactions on the 1-Wire bus begin with an initial-
ization sequence. The initialization sequence consists
of a reset pulse transmitted by the bus master followed
by presence pulse(s) transmitted by the slave(s). The
presence pulse lets the bus master know that the
DS1923 is on the bus and is ready to operate. For more
details, see the
1-Wire Signaling
section.
1-Wire ROM Function Commands
Once the bus master has detected a presence, it can
issue one of the eight ROM function commands that the
DS1923 supports. All ROM function commands are 8
bits long. A list of these commands follows (see the
flowchart in Figure 11).
Read ROM [33h]
This command allows the bus master to read the
DS1923’s 8-bit family code, unique 48-bit serial number,
and 8-bit CRC. This command can only be used if there
is a single slave on the bus. If more than one slave is pre-
sent on the bus, a data collision occurs when all slaves
try to transmit at the same time (open drain produces a
wired-AND result). The resultant family code and 48-bit
serial number results in a mismatch of the CRC.
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM
sequence, allows the bus master to address a specific
DS1923 on a multidrop bus. Only the DS1923 that exact-
ly matches the 64-bit ROM sequence responds to the fol-
lowing memory function command. All other slaves wait
for a reset pulse. This command can be used with a sin-
gle device or multiple devices on the bus.
Search ROM [F0h]
When a system is initially brought up, the bus master
might not know the number of devices on the 1-Wire
bus or their registration numbers. By taking advantage
of the wired-AND property of the bus, the master can
use a process of elimination to identify the registration
numbers of all slave devices. For each bit of the regis-
tration number, starting with the least significant bit, the
bus master issues a triplet of time slots. On the first slot,
each slave device participating in the search outputs
the true value of its registration number bit. On the sec-
ond slot, each slave device participating in the search
outputs the complemented value of its registration num-
ber bit. On the third slot, the master writes the true
value of the bit to be selected. All slave devices that do
not match the bit written by the master stop participat-
ing in the search. If both of the read bits are zero, the
master knows that slave devices exist with both states
of the bit. By choosing which state to write, the bus
master branches in the ROM code tree. After one com-
plete pass, the bus master knows the registration num-
ber of a single device. Additional passes identify the
registration numbers of the remaining devices. Refer to
Application Note 187:
1-Wire Search Algorithm
for a
detailed discussion, including an example.
Conditional Search ROM [ECh]
The Conditional Search ROM command operates simi-
larly to the Search ROM command except that only
those devices that fulfill certain conditions participate in
the search. This function provides an efficient means
for the bus master to identify devices on a multidrop
system that have to signal an important event. After
each pass of the conditional search that successfully
determined the 64-bit ROM code for a specific device
on the multidrop bus, that particular device can be indi-
vidually accessed as if a Match ROM had been issued,
since all other devices have dropped out of the search
process and are waiting for a reset pulse.
The DS1923 responds to the Conditional Search ROM
command if one of the five alarm flags of the Alarm
Status register (address 0214h) reads 1. The humidity
and temperature alarm only occurs if enabled (see the
Temperature Sensor Alarm
and
Humidity Alarm
sec-
tions). The BOR alarm is always enabled. The first
alarm that occurs makes the device respond to the
Conditional Search ROM command.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 38www.maximintegrated.com
Skip ROM [CCh]
This command can save time in a single-drop bus sys-
tem by allowing the bus master to access the memory
functions without providing the 64-bit ROM code. For
example, if more than one slave is present on the bus
and a read command is issued following the Skip ROM
command, data collision occurs on the bus as multiple
slaves transmit simultaneously (open-drain pulldowns
produce a wired-AND result).
Resume [A5h]
The DS1923 must be accessed several times before a
mission starts. In a multidrop environment this means
that the 64-bit ROM code after a Match ROM command
must be repeated for every access. To maximize the
data throughput in a multidrop environment, the Resume
command was implemented. This command checks the
status of the RC bit and, if it is set, directly transfers con-
trol to the memory/control functions, similar to a Skip
ROM command. The only way to set the RC bit is
through successfully executing the Match ROM, Search
ROM, or Overdrive-Match ROM command. Once the RC
bit is set, the device can repeatedly be accessed
through the Resume command. Accessing another
device on the bus clears the RC bit, preventing two or
more devices from simultaneously responding to the
Resume command.
Overdrive-Skip ROM [3Ch]
On a single-drop bus this command can save time by
allowing the bus master to access the memory/control
functions without providing the 64-bit ROM code. Unlike
the normal Skip ROM command, the Overdrive-Skip
ROM command sets the DS1923 in the overdrive mode
(OD = 1). All communication following this command
must occur at overdrive speed until a reset pulse of
minimum 690μs duration resets all devices on the bus
to standard speed (OD = 0).
When issued on a multidrop bus, this command sets all
overdrive-supporting devices into overdrive mode. To
subsequently address a specific overdrive-supporting
device, a reset pulse at overdrive speed must be
issued followed by a Match ROM or Search ROM com-
mand sequence. This speeds up the time for the
search process. If more than one slave supporting
overdrive is present on the bus and the Overdrive-Skip
ROM command is followed by a read command, data
collision occurs on the bus as multiple slaves transmit
simultaneously (open-drain pulldowns produce a wired-
AND result).
Overdrive-Match ROM [69h]
The Overdrive-Match ROM command followed by a
64-bit ROM sequence transmitted at overdrive speed
allows the bus master to address a specific DS1923 on
a multidrop bus and to simultaneously set it in overdrive
mode. Only the DS1923 that exactly matches the 64-bit
ROM sequence responds to the subsequent
memory/control function command. Slaves already in
overdrive mode from a previous Overdrive-Skip ROM or
successful Overdrive-Match ROM command remain in
overdrive mode. All overdrive-capable slaves return to
standard speed at the next reset pulse of minimum
690μs duration. The Overdrive-Match ROM command
can be used with a single or multiple devices on the
bus.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 39www.maximintegrated.com
DS1923 Tx
PRESENCE PULSE
BUS MASTER Tx
RESET PULSE
BUS MASTER Tx ROM
FUNCTION COMMAND
DS1923 Tx
CRC BYTE
DS1923 Tx
FAMILY CODE
(1 BYTE)
DS1923 Tx
SERIAL NUMBER
(6 BYTES)
OD = 0
RC = 0
MASTER Tx BIT 0
RC = 0 RC = 0 RC = 0
Y
OD
RESET PULSE?
YY
Y
Y
Y
Y
N
33h
READ ROM
COMMAND?
N55h
MATCH ROM
COMMAND?
BIT 0 MATCH? BIT 0 MATCH?
N
N N
N N
N N
F0h
SEARCH ROM
COMMAND?
NECh
CONDITIONAL SEARCH
COMMAND?
N
Y
RC = 1
MASTER Tx BIT 1
MASTER Tx BIT 63
BIT 1 MATCH?
BIT 63 MATCH?
Y
Y
RC = 1
FROM MEMORY/CONTROL
FUNCTION FLOWCHART (FIGURE 9)
DS1923 Tx BIT 0
DS1923 Tx BIT 0
MASTER Tx BIT 0
BIT 1 MATCH?
BIT 63 MATCH?
DS1923 Tx BIT 1
DS1923 Tx BIT 1
MASTER Tx BIT 1
DS1923 Tx BIT 63
DS1923 Tx BIT 63
MASTER Tx BIT 63
Y
BIT 0 MATCH?
N
N
N
Y
Y
RC = 1
DS1923 Tx BIT 0
DS1923 Tx BIT 0
MASTER Tx BIT 0
CONDITION
MET?
N
Y
BIT 1 MATCH?
BIT 63 MATCH?
DS1923 Tx BIT 1
DS1923 Tx BIT 1
MASTER Tx BIT 1
DS1923 Tx BIT 63
DS1923 Tx BIT 63
MASTER Tx BIT 63
Y
FROM FIGURE 11b
TO FIGURE 11b
TO FIGURE 11b
FROM FIGURE 11b
TO MEMORY/CONTROL
FUNCTION FLOWCHART (FIGURE 9)
Figure 11a. ROM Functions Flowchart
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 40www.maximintegrated.com
MASTER Tx BIT 0
RC = 0; OD = 1 RC = 0; OD = 1
OD = 0
(SEE NOTE)
NOTE: THE OD FLAG REMAINS AT 1 IF THE DEVICE WAS ALREADY AT OVERDRIVE SPEED BEFORE THE OVERDRIVE-MATCH ROM COMMAND WAS ISSUED.
(SEE NOTE)
(SEE NOTE)
RC = 1?
Y
N
Y
A5h
RESUME
COMMAND?
N
Y
3Ch
OVERDRIVE-
SKIP ROM?
N
RC = 0
Y
CCh
SKIP ROM
COMMAND?
Y
69h
OVERDRIVE-
MATCH ROM?
N
N
OD = 0
N
OD = 0
N
MASTER Tx BIT 1
MASTER Tx BIT 63
Y
Y
RC = 1
Y
BIT 0 MATCH?
MASTER Tx
RESET?
BIT 63 MATCH?
BIT 1 MATCH?
N
Y
N
Y
MASTER Tx
RESET?
N
TO FIGURE 11a
FROM FIGURE 11a
FROM FIGURE 11a
TO FIGURE 11a
Figure 11b. ROM Functions Flowchart (continued)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 41www.maximintegrated.com
1-Wire Signaling
The DS1923 requires strict protocols to ensure data
integrity. The protocol consists of four types of signaling
on one line: reset sequence with reset pulse and pres-
ence pulse, write-zero, write-one, and read-data. Except
for the presence pulse, the bus master initiates all these
signals. The DS1923 can communicate at two different
speeds: standard speed and overdrive speed. If not
explicitly set into the overdrive mode, the DS1923 com-
municates at standard speed. While in overdrive mode
the fast timing applies to all waveforms.
To get from idle to active, the voltage on the 1-Wire line
needs to fall from VPUP below the threshold VTL. To get
from active to idle, the voltage needs to rise from
VILMAX past the threshold VTH. The time it takes for the
voltage to make this rise is seen in Figure 12 as “ε” and
its duration depends on the pullup resistor (RPUP) used
and the capacitance of the 1-Wire network attached.
The voltage VILMAX is relevant for the DS1923 when
determining a logical level, not triggering any events.
The initialization sequence required to begin any com-
munication with the DS1923 is shown in Figure 12. A
reset pulse followed by a presence pulse indicates the
DS1923 is ready to receive data, given the correct ROM
and memory function command. If the bus master uses
slew-rate control on the falling edge, it must pull down
the line for tRSTL + tFto compensate for the edge. A
tRSTL duration of 690μs or longer exits the overdrive
mode, returning the device to standard speed. If the
DS1923 is in overdrive mode and tRSTL is no longer
than 80μs, the device remains in overdrive mode.
After the bus master has released the line, it goes into
receive mode (Rx). Now the 1-Wire bus is pulled to
VPUP through the pullup resistor or, in the case of a
DS2480B driver, through active circuitry. When the
threshold VTH is crossed, the DS1923 waits for tPDH
and then transmits a presence pulse by pulling the line
low for tPDL. To detect a presence pulse, the master
must test the logical state of the 1-Wire line at tMSP.
The tRSTH window must be at least the sum of
tPDHMAX, tPDLMAX, and tRECMIN. Immediately after
tRSTH is expired, the DS1923 is ready for data commu-
nication. In a mixed population network, tRSTH should
be extended to minimum 480μs at standard speed and
48μs at overdrive speed to accommodate other 1-Wire
devices.
Read/Write Time Slots
Data communication with the DS1923 takes place in
time slots that carry a single bit each. Write time slots
transport data from bus master to slave. Read time slots
transfer data from slave to master. The definitions of the
write and read time slots are illustrated in Figure 13.
All communication begins with the master pulling the
data line low. As the voltage on the 1-Wire line falls
below the threshold VTL, the DS1923 starts its internal
timing generator that determines when the data line is
sampled during a write time slot and how long data is
valid during a read time slot.
RESISTOR MASTER DS1923
tRSTL tPDL
tRSTH
tPDH
MASTER Tx "RESET PULSE" MASTER Rx "PRESENCE PULSE"
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
ε
tF
tREC
tMSP
Figure 12. Initialization Procedure: Reset and Presence Pulse
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 42www.maximintegrated.com
Master-to-Slave
For a write-one time slot, the voltage on the data line
must have crossed the VTH threshold before the write-one
low time tW1LMAX is expired. For a write-zero time slot,
the voltage on the data line must stay below the VTH
threshold until the write-zero low time tW0LMIN is expired.
The voltage on the data line should not exceed VILMAX
during the entire tW0L or tW1L window. After the VTH
threshold has been crossed, the DS1923 needs a recov-
ery time tREC before it is ready for the next time slot.
Slave-to-Master
A read-data time slot begins like a write-one time slot.
The voltage on the data line must remain below VTL
until the read low time tRL is expired. During the tRL
window, when responding with a 0, the DS1923 starts
pulling the data line low; its internal timing generator
determines when this pulldown ends and the voltage
starts rising again. When responding with a 1, the
DS1923 does not hold the data line low at all, and the
voltage starts rising as soon as tRL is over.
The sum of tRL + δ(rise time) on one side and the inter-
nal timing generator of the DS1923 on the other side
define the master sampling window (tMSRMIN to
tMSRMAX) in which the master must perform a read from
the data line. For most reliable communication, tRL
should be as short as permissible and the master
should read close to but no later than tMSRMAX. After
reading from the data line, the master must wait until
tSLOT is expired. This guarantees sufficient recovery
time tREC for the DS1923 to get ready for the next time
slot.
Improved Network
Behavior(Switchpoint Hysteresis)
In a 1-Wire environment, line termination is possible
only during transients controlled by the bus master (1-
Wire driver). 1-Wire networks, therefore, are susceptible
to noise of various origins. Depending on the physical
size and topology of the network, reflections from end
points and branch points can add up or cancel each
other to some extent. Such reflections are visible as
glitches or ringing on the 1-Wire communication line.
Noise coupled onto the 1-Wire line from external
sources can also result in signal glitching. A glitch dur-
ing the rising edge of a time slot can cause a slave
device to lose synchronization with the master and, as
a consequence, result in a Search ROM command
coming to a dead end or cause a device-specific func-
tion command to abort. For better performance in net-
work applications, the DS1923 uses a new 1-Wire
front-end, which makes it less sensitive to noise and
also reduces the magnitude of noise injected by the
slave device itself.
The DS1923’s 1-Wire front-end differs from traditional
slave devices in four characteristics:
1) The falling edge of the presence pulse has a con-
trolled slew rate. This provides a better match to the
line impedance than a digitally switched transistor,
converting the high-frequency ringing known from
traditional devices into a smoother, low-bandwidth
transition. The slew-rate control is specified by the
parameter tFPD, which has different values for stan-
dard and overdrive speed.
2) There is additional lowpass filtering in the circuit that
detects the falling edge at the beginning of a time
slot. This reduces the sensitivity to high-frequency
noise. This additional filtering does not apply at over-
drive speed.
3) There is a hysteresis at the low-to-high switching
threshold VTH. If a negative glitch crosses VTH but
does not go below VTH - VHY, it is not recognized
(Figure 14, Case A). The hysteresis is effective at
any 1-Wire speed.
4) There is a time window specified by the rising edge
hold-off time tREH during which glitches are ignored,
even if they extend below VTH - VHY threshold
(Figure 14, Case B, tGL < tREH). Deep voltage
droops or glitches that appear late after crossing the
VTH threshold and extend beyond the tREH window
cannot be filtered out and are taken as the begin-
ning of a new time slot (Figure 14, Case C, tGL ≥
tREH).
Devices that have the parameters tFPD, VHY, and tREH
specified in their electrical characteristics use the
improved 1-Wire front-end.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 43www.maximintegrated.com
RESISTOR MASTER
RESISTOR MASTER
RESISTOR MASTER DS1923
ε
ε
δ
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
tSLOT
tW1L
tREC
tSLOT
tSLOT
tW0L
tREC
MASTER
SAMPLING
WINDOW
tRL
tMSR
WRITE-ONE TIME SLOT
WRITE-ZERO TIME SLOT
READ-DATA TIME SLOT
Figure 13. Read/Write Timing Diagrams
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 44www.maximintegrated.com
VPUP
VTH VHY
0V
tREH
tGL
tREH
tGL
CASE A CASE CCASE B
Figure 14. Noise Suppression Scheme
1ST
STAGE
2ND
STAGE
3RD
STAGE
4TH
STAGE
7TH
STAGE
8TH
STAGE
6TH
STAGE
5TH
STAGE
X0X1X2X3X4
POLYNOMIAL = X16 + X15 + X2 + 1
INPUT DATA
CRC OUTPUT
X5X6
11TH
STAGE
12TH
STAGE
15TH
STAGE
14TH
STAGE
13TH
STAGE
X11 X12
9TH
STAGE
10TH
STAGE
X9X10 X13 X14
X7
16TH
STAGE
X16
X15
X8
Figure 15. CRC-16 Hardware Description and Polynomial
CRC Generation
The DS1923 uses two types of CRCs. One CRC is an
8-bit type and is stored in the most significant byte of
the 64-bit ROM. The bus master can compute a CRC
value from the first 56 bits of the 64-bit ROM and com-
pare it to the value stored within the DS1923 to deter-
mine if the ROM data has been received error-free. The
equivalent polynomial function of this CRC is
X8+X
5+X
4+ 1. This 8-bit CRC is received in the true
(noninverted) form, and it is computed at the factory
and lasered into the ROM.
The other CRC is a 16-bit type, generated according to
the standardized CRC-16 polynomial function
X16 +X
15 + X2+ 1. This CRC is used for error detec-
tion when reading register pages or the data-log mem-
ory using the Read Memory with CRC command and
for fast verification of a data transfer when writing to or
reading from the scratchpad. In contrast to the 8-bit
CRC, the 16-bit CRC is always communicated in the
inverted form. A CRC generator inside the DS1923
(Figure 15) calculates a new 16-bit CRC as shown in
the command flowchart of Figure 9. The bus master
compares the CRC value read from the device to the
one it calculates from the data and decides whether to
continue with an operation or to reread the portion of
the data with the CRC error. With the initial pass
through the Read Memory with CRC flowchart, the 16-
bit CRC value is the result of shifting the command byte
into the cleared CRC generator, followed by the 2
address bytes and the data bytes. The password is
excluded from the CRC calculation. Subsequent pass-
es through the Read Memory with CRC flowchart gen-
erate a 16-bit CRC that is the result of clearing the CRC
generator and then shifting in the data bytes.
With the Write Scratchpad command, the CRC is gener-
ated by first clearing the CRC generator and then shift-
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 45www.maximintegrated.com
ing in the command code, the target addresses TA1
and TA2, and all the data bytes. The DS1923 transmits
this CRC only if the data bytes written to the scratchpad
include scratchpad ending offset 11111b. The data can
start at any location within the scratchpad.
With the Read Scratchpad command, the CRC is gen-
erated by first clearing the CRC generator and then
shifting in the command code, the target addresses
TA1 and TA2, the E/S byte, and the scratchpad data
starting at the target address. The DS1923 transmits
this CRC only if the reading continues through the end
of the scratchpad, regardless of the actual ending off-
set. For more information on generating CRC values,
refer to Application Note 27.
Command-Specific 1-Wire Communication Protocol—Legend
SYMBOL DESCRIPTION
RST 1-Wire reset pulse generated by master.
PD 1-Wire presence pulse generated by slave.
Select Command and data to satisfy the ROM function protocol.
WS Command “Write Scratchpad.”
RS Command “Read Scratchpad.”
CPS Command “Copy Scratchpad with Password.”
RMC Command “Read Memory with Password and CRC.”
CM Command “Clear Memory with Password.”
FC Command “Forced Conversion.”
SM Command “Start Mission with Password.”
STP Command “Stop Mission with Password.”
TA Target Address TA1, TA2.
TA–E/S Target Address TA1, TA2 with E/S byte.
<Data to EOS> Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh.
<Data to EOP> Transfer of as many data bytes as are needed to reach the end of a memory page.
<Data to EOM> Transfer as many bytes as are needed to reach the end of the data-log memory.
<PW/Dummy> Transfer of 8 bytes that either represent a valid password or acceptable dummy data.
<32 Bytes> Transfer of 32 bytes.
<Data> Transfer of an undetermined amount of data.
FFh Transmission of one FFh byte.
CRC-16 Transfer of an inverted CRC-16.
FF Loop Indefinite loop where the master reads FF bytes.
AA Loop Indefinite loop where the master reads AA bytes.
Busy Interval during Copy Scratchpad where the DS1923 does not respond. Any bits read during this time
are logic 1.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 46www.maximintegrated.com
RST
Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)
PD WS TASelect CRC-16 FF Loop<Data to EOS>
CRC-16 FF Loop
CRC-16
RST
Read Scratchpad (Cannot Fail)
PD RS TA-E/SSelect <Data to EOS>
Busy AA LoopRST
Copy Scratchpad with Password (Success)
PD CPS TA-E/SSelect <PW/Dummy>
FF Loop
FF Loop
Loop
RST
Copy Scratchpad with Password (Fail TA-E/S or Password)
PD CPS TA-E/SSelect <PW/Dummy>
FF Loop
FF Loop
RST
Read Memory with Password and CRC (Fail Password or Address)
PD RMC
FFh
Select <PW/Dummy>
RST TA
TA
Read Memory with Password and CRC (Success)
PD RMCSelect <PW/Dummy> <Data to EOP>
RST CM
Clear Memory with Password
PD Select <PW/Dummy>
CRC-16
<32 Bytes>
To verify success, read the General Status register at address 0215h. If MEMCLR is 1, the command was
executed successfully.
Command-Specific 1-Wire Communication Protocol—Color Codes
Master-to-Slave Slave-to-Master
1-Wire Communication Examples
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 47www.maximintegrated.com
Mission Example: Prepare
and Start a New Mission
Assumption: The previous mission has been ended by
using the Stop Mission command. Passwords are not
enabled. The device is a DS1923.
Starting a mission requires three steps:
Step 1: Clear the data of the previous mission.
Step 2: Write the setup data to register page 1.
Step 3: Start the new mission.
Step 1: Clear the data of the previous mission.
With only a single device connected to the bus master,
the communication of step 1 looks like this:
RST
Forced Conversion
PD FCSelect FF LoopFFh
To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Samples
Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully.
FF LoopRST
Start Mission with Password
PD SMSelect <PW/Dummy> FFh
To verify success, read the General Status register at address 0215h. If MIP is 1 and MEMCLR is 0, the command
was executed successfully.
RST
Stop Mission with Password
PD STPSelect FF Loop<PW/Dummy> FFh
To verify success, read the General Status register at address 0215h. If MIP is 0, the command was executed
successfully.
1-Wire Communication Examples (continued)
MASTER MODE DATA (LSB FIRST) COMMENTS
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Tx CCh Issue “Skip ROM” command
Tx 96h Issue “Clear Memory” command
Tx <8 FFh bytes> Send dummy password
Tx FFh Send dummy byte
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 48www.maximintegrated.com
Step 2: Write the setup data to register page 1.
During the setup, the device needs to learn the follow-
ing information:
• Time and Date
• Sample Rate
• Alarm Thresholds
• Alarm Controls (Response to Conditional Search ROM)
• General Mission Parameters (e.g., Channels to Log
and Logging Format, Rollover, Start Mode)
• Mission Start Delay
The following data sets up the DS1923 for a mission
that logs temperature and humidity using 8-bit format
for both.
ADDRESS DATA EXAMPLE VALUES FUNCTION
0200h 00h
0201h 30h
0202h 15h
15:30:00 hours Time
0203h 15h
0204h 05h
0205h 04h
15th of May in 2004 Date
0206h 0Ah
0207h 00h
Every 10 minutes (EHSS = 0) Sample rate
0208h 66h
0209h 7Ah
10°C Low
20°C High Temperature Alarm Thresholds
020Ah 6Fh
020Bh 9Eh
40%RH Low
70%RH High
Humidity Alarm Threshold, no software
correction used
020Ch FFh
020Dh FFh
020Eh FFh
020Fh FFh
(Don’t care) Clock through read-only registers
0210h 03h Enable high and low alarm Temperature Alarm Control
0211h FFh Enable high and low alarm Humidity Alarm Control
0212h 01h On (enabled), EHSS = 0 (low sample rate) RTC Oscillator Control, sample rate selection
0213h C3h Normal start; no rollover; 8-bit logging General Mission Control
0214h FFh
0215h FFh
(Don’t care) Clock through read-only registers
0216h 5Ah
0217h 00h
0218h 00h
90 minutes Mission Start Delay
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 49www.maximintegrated.com
With only a single device connected to the bus master,
the communication of step 2 looks like this:
MASTER MODE DATA (LSB FIRST) COMMENTS
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Tx CCh Issue “Skip ROM” command
Tx 0Fh Issue “Write Scratchpad” command
Tx 00h TA1, beginning offset = 00h
Tx 02h TA2, address = 0200h
Tx <25 Data Bytes> Write 25 bytes of data to scratchpad
Tx <7 FFh Bytes> Write through the end of the scratchpad
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Tx CCh Issue “Skip ROM” command
Tx AAh Issue “Read Scratchpad” command
Rx 00h Read TA1, beginning offset = 00h
Rx 02h Read TA2, address = 0200h
Rx 1Fh Read E/S, ending offset = 1Fh, flags = 0h
Rx <32 Data Bytes> Read scratchpad data and verify
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Tx CCh Issue “Skip ROM” command
Tx 99h Issue “Copy Scratchpad” command
Tx 00h TA1
Tx 02h TA2
Tx 1Fh E/S
(AUTHORIZATION CODE)
Tx <8 FFh Bytes> Send dummy password
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
MASTER MODE DATA (LSB FIRST) COMMENTS
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Tx CCh Issue “Skip ROM” command
Tx CCh Issue “Start Mission” command
Tx <8 FFh Bytes> Send dummy password
Tx FFh Send dummy byte
Tx (Reset) Reset pulse
Rx (Presence) Presence pulse
Step 3: Start the new mission.
With only a single device connected to the bus master,
the communication of step 3 looks like this:
If step 3 was successful, the MIP bit in the General
Status register is 1, the MEMCLR bit is 0, and the
Mission Start Delay counts down.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 50www.maximintegrated.com
Software Correction Algorithm
for Temperature
The accuracy of high-resolution temperature conver-
sion results (forced conversion as well as temperature
logs) can be improved through a correction algorithm.
The data needed for this software correction is stored in
the calibration memory (memory page 18). It consists of
reference temperature (Tr) and conversion result (Tc)
for two different temperatures, as shown below. See the
Temperature Conversion
section for the binary number
format.
The software correction algorithm requires two addition-
al values, which are not stored in the device. For the
DS1923 these values are Tr1 = 60°C and Offset = 41.
The correction algorithm consists of two steps, prepara-
tion and execution. The preparation step first converts
temperature data from binary to decimal °C format.
Next, three coefficients A, B, and C are computed. In
the execution step, the temperature reading as deliv-
ered by the DS1923 is first converted from the low/high-
byte format (TcL, TcH) to °C (Tc) and then corrected to
Tcorr. Once step 1 is performed, the three coefficients
can be used repeatedly to correct any temperature
reading and temperature log of
the same device
.
ADDRESS DESIGNATOR DESCRIPTION
0240h Tr2H Cold reference temperature, high-byte.
0241h Tr2L Cold reference temperature, low-byte.
0242h Tc2H Conversion result at cold reference temperature, high-byte.
0243h Tc2L Conversion result at cold reference temperature, low-byte.
0244h Tr3H Hot reference temperature, high-byte.
0245h Tr3L Hot reference temperature, low-byte.
0246h Tc3H Conversion result at hot reference temperature, high-byte.
0247h Tc3L Conversion result at hot reference temperature, low-byte.
Step 1: Preparation
Tr1 = 60
Offset = 41
Tr2 = Tr2H/2 + Tr2L/512 - Offset (convert from binary to °C)
Tr3 = Tr3H/2 + Tr3L/512 - Offset (convert from binary to °C)
Tc2 = Tc2H/2 + Tc2L/512 - Offset (convert from binary to °C)
Tc3 = Tc3H/2 + Tc3L/512 - Offset (convert from binary to °C)
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr22- Tr12) x (Err3 - Err1)/[(Tr22- Tr12) x (Tr3 - Tr1) + (Tr32- Tr12) x (Tr1 - Tr2)]
A = B x (Tr1 - Tr2)/(Tr22- Tr12)
C = Err1 - A x Tr12- B x Tr1
Step 2: Execution
Tc = TcH/2 + TcL/512 - Offset (convert from binary to °C)
Tcorr = Tc - (A x Tc2+ B x Tc + C) (the actual correction)
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 51www.maximintegrated.com
Software Correction Algorithm
for Humidity
The accuracy of humidity conversion results (forced
conversion as well as logged data) can be improved
through a correction algorithm. The data needed for
this software correction is stored in the calibration
memory (memory page 18). It consists of reference
humidity (Hr) and conversion result (Hc) for three differ-
ent humidity levels, as shown below. The data is taken
at 25°C.
The correction algorithm consists of two steps: prepara-
tion and execution. The preparation step first converts
humidity data from binary to decimal %RH format. Next,
three coefficients A, B, and C are computed. In the exe-
cution step the humidity reading as delivered by the
DS1923 (raw data) is first converted from the low/high-
byte format (HcL, HcH) to %RH (Hc) and then correct-
Numerical Temperature Correction Example
CONVERTED DATA FROM CALIBRATION MEMORY ERROR VALUES
Tr2 = -10.1297°C
Tr3 = 24.6483°C
Tc2 = -10.0625°C
Tc3 = 24.5°C
Err2 = 0.0672°C
Err3 = -0.1483°C
Err1 = Err2
RESULTING CORRECTION COEFFICIENTS APPLICATION OF CORRECTION COEFFICIENTS
TO SAMPLE READING
B = -0.008741
A = 0.000175/°C
C = -0.039332°C
Tc = 22.500000°C
Tcorr = 22.647275°C
Note: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are
found on various websites and are included in cross-compilers.
ADDRESS DESIGNATOR DESCRIPTION
0248h Hr1H Low reference humidity, high byte.
0249h Hr1L Low reference humidity, low byte.
024Ah Hc1H Conversion result at low reference humidity, high byte.
024Bh Hc1L Conversion result at low reference humidity, low byte.
024Ch Hr2H Medium reference humidity, high byte.
024Dh Hr2L Medium reference humidity, low byte.
024Eh Hc2H Conversion result at medium reference humidity, high byte.
024Fh Hc2L Conversion result at medium reference humidity, low byte.
0250h Hr3H High reference humidity, high byte.
0251h Hr3L High reference humidity, low byte.
0252h Hc3H Conversion result at high reference humidity, high byte.
0253h Hc3L Conversion result at high reference humidity, low byte.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 52www.maximintegrated.com
ed to Hcorr. Once step 1 is performed, the three coefficients can be used repeatedly to correct any humidity reading
and humidity log of
the same device
.
Step 1: Preparation
For the humidity data in the calibration memory, the lower 4 bits of each low byte are set to 0. This simplifies the con-
version from the binary data format to raw %RH values to a one-line equation.
Hr1 = ((Hr1H x 256 + Hr1L) x 5.02/65536 - 0.958)/0.0307 (convert from binary to %RH)
Hr2 = ((Hr2H x 256 + Hr2L) x 5.02/65536 - 0.958)/0.0307
Hr3 = ((Hr3H x 256 + Hr3L) x 5.02/65536 - 0.958)/0.0307
Hc1 = ((Hc1H x 256 + Hc1L) x 5.02/65536 - 0.958)/0.0307
Hc2 = ((Hc2H x 256 + Hc2L) x 5.02/65536 - 0.958)/0.0307
Hc3 = ((Hc3H x 256 + Hc3L) x 5.02/65536 - 0.958)/0.0307
Err1 = Hc1 - Hr1
Err2 = Hc2 - Hr2
Err3 = Hc3 - Hr3
B = [(Hr22- Hr12) x (Err3 - Err1) + Hr32x (Err1 - Err2) + Hr12x (Err2 - Err1)]/[(Hr22- Hr12) x (Hr3 - Hr1) +
(Hr32- Hr12) x (Hr1 - Hr2)]
A = [Err2 - Err1 + B x (Hr1 - Hr2)]/(Hr22- Hr12)
C = Err1 - A x Hr12- B x Hr1
Step 2: Execution
Numerical Humidity Correction Example
CONVERTED DATA FROM CALIBRATION MEMORY ERROR VALUES
Hr1 = 20%RH
Hr2 = 60%RH
Hr3 = 90%RH
Hc1 = 17.65%RH
Hc2 = 56.41%RH
Hc3 = 89.57%RH
Err1 = -2.35%RH
Err2 = -3.59%RH
Err3 = -0.43%RH
RESULTING CORRECTION COEFFICIENTS APPLICATION OF CORRECTION COEFFICIENTS
TO SAMPLE READING
B = -0.186810
A = 0.001948%RH
C = 0.607143%RH
Hc = 8.9%RH
Hcorr = 9.8%RH
Note: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are
found on various websites and are included in cross-compilers.
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 53www.maximintegrated.com
Hc = ((HcH x 256 + HcL) x 5.02/65536 - 0.958)/0.0307
(convert from binary to %RH)
Hcorr = Hc - (A x Hc2+ B x Hc + C)
(the actual correction)
RH Temperature Compensation
The data for the software correction of humidity is taken
at 25°C. Since the temperature characteristics of the
humidity sensor are known, humidity readings taken at
other temperatures can be corrected, provided the
temperature at the time of the humidity conversion is
also known. Therefore, to obtain the most accurate
humidity results, both temperature and humidity should
be logged.
Temperature compensation uses the following equation:
HTcorr = (Hcorr x K + αx (T - 25°C)
- βx (T - 25°C)2)/(K + γx (T - 25°C) - δx (T - 25°C)2)
NAME FUNCTION VALUE
T Temperature at the time of humidity conversion. (in °C)
K Humidity sensor conversion constant. 0.0307
Linear compensation, enumerator. 0.0035/°C
Quadratic compensation, enumerator. 0.000043/°C2
Linear compensation, denominator. >15°C: 0.00001/°C
15°C: -0.00005/°C
Quadratic compensation, denominator. 0.000002/°C2
SAMPLE INPUT DATA APPLICATION OF CORRECTION COEFFICIENTS TO SAMPLE READING
T = 70°C
Hcorr = 24.445%RH
= 0.00001/°C
HTcorr = (24.445 x 0.0307 + 0.0035 x 45 - 0.000043 x 452)/(0.0307 + 0.00001 x 45 - 0.000002 x 452)
HTcorr = 30.291%
Numerical RH Temperature Compensation Example
Hcorr is the humidity reading with the software correc-
tion algorithm for humidity already applied, as
explained in the previous section. The function and val-
ues of the other parameters are explained in the table
below.
Software Saturation Drift
Compensation
Capacitive humidity sensors read higher humidity val-
ues than the actual humidity level when they are
exposed to a high-humidity environment for an extend-
ed time period. The DS1923’s humidity sensor pro-
duces readings that are higher than the actual humidity
when exposed to humidity levels of about 70%RH and
higher. This shift continues to increase while the device
remains at 70%RH and above. This effect is called sat-
uration drift, or hysteresis. This drift is reversible.
Readings return to their regular level when the DS1923
is removed from a high-humidity environment.
It is possible to compensate for most of the error intro-
duced by the saturation drift by post-processing tem-
perature and humidity logs using the equation below,
which is based on laboratory tests and curve-fitting
techniques.
ARHkThe average software-corrected and tempera-
ture-compensated humidity reading of the kth
hour that the device is continuously exposed
to 70%RH or higher.
TkThe average software-corrected temperature
reading of the kth hour that the device is
continuously exposed to 70%RH or higher.
N The number of hours that the device is contin-
uously exposed to 70%RH or higher.
HTcorr The humidity reading at the end of the Nth
hour with the software correction algorithm for
humidity and temperature compensation
already applied. See the
Software Correction
HScorr HTcorr ARHkk
=− ××
+
−×
0 0156 2 54
1
0 3502
..
.
TTk
k
N
−
()
∑
=25 100
1/
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 54www.maximintegrated.com
Algorithm for Humidity
and
RH Temperature
Compensation
sections for details.
The numbers in the equation are derived from curve fit-
ting. They apply to a time scale in hours.
HScorr = HTcorr - Sum of partial corrections
= 93.70207%RH - 3.458875%RH
HScorr = 90.24319%RH
The data in this example was taken from devices that
were exposed for several hours to 90%RH at 25°C in a
test chamber. The drift per hour decreases the longer
the device is exposed to high humidity. The correction
algorithm compensates for the drift reasonably well. For
some applications, compensation may not be neces-
sary since the error introduced by the saturation is rela-
tively small.
SAMPLE INPUT DATA (N = 8) APPLICATION OF CORRECTION ALGORITHM
k (HOUR) Tk (°C) ARHk (%RH) PARTIAL CORRECTIONS (INDIVIDUAL ADDENDS)
1 25.1 91.1 1.024321
2 25.0 92.5 0.751140
3 24.9 92.9 0.544824
4 25.0 93.1 0.393535
5 25.1 93.2 0.283950
6 25.1 93.3 0.205086
7 25.0 93.6 0.148591
8 24.9 93.7 0.107428
HTcorr = 93.70207%RH Sum of partial corrections: 3.458875
Numerical Saturation Drift Compensation Example
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated | 55www.maximintegrated.com
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16.25mm
5.89mm
0.51mm
17.35mm
FRONT-SIDE BRANDING
GND
IO
A1 41
000000FBC52B
1-Wire®
Hygrochron™
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5
BACK-SIDE BRANDING
®
Pin Configuration
Package Information
For the latest package outline information and land patterns (foot-
prints), go to www.maximintegrated.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but the
drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
F5 Can IB#6HB 21-0266 —
Common iButton Can Features
•Rugged Chip-Based Data Carrier with Fast, Simple
Access to Information
•Digital Identification and Information by
Momentary Contact
•Unique Factory-Lasered 64-Bit Registration
Number Ensures Error-Free Device Selection
and Absolute Traceability Because No Two Parts
Are Alike
•Built-In Multidrop Controller for 1-Wire Net
•Chip-Based Data Carrier Compactly Stores
Information
•Data Can Be Accessed While Affixed to an Object
•Button Shape is Self-Aligning with Cup-Shaped
Probes
•Durable Stainless-Steel Case Engraved with
Registration Number Withstands Harsh
Environments
•Easily Affixed with Self-Stick Adhesive Backing,
Latched by Its Flange, or Locked with a Ring
Pressed Onto Its Rim
•Presence Detector Acknowledges When Reader
First Applies Voltage
DS1923 iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and
max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. © 2015 Maxim Integrated Products, Inc. | 56
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.
Revision History
REVISION
NUMBER
REVISION
DATE DESCRIPTION PAGES
CHANGED
0 8/04 Initial release —
1 12/07
Changed bullet from “Hydrophobic Filter Protects Sensor Against Dust, Dirt, Water, and
Contaminants” to “Hydrophobic Filter Protects Sensor Against Dust, Dirt, Contaminants,
and Water Droplets/Condensation”; deleted “Application Pending” from UL bullet and
safety statement; added text to the Application section: Note that the initial sealing level of
DS1923 achieves IP56. Aging and use conditions can degrade the integrity of the seal
over time, so for applications with significant exposure to liquids, sprays, or other similar
environments, it is recommended to place the Hygrochron under a shield to protect it.
(See www.maximintegrated.com/AN4126). The hydrophobic filter may not protect the
DS1923 from destruction in the event of full submersion in liquid
1, 4, 10
2 4/09 Created newer template-style data sheet All
3 10/09 Deleted the standard part number from the Ordering Information table 1
4 4/11
Updated UL certificate reference; added “Guaranteed by design” note to Electrical
Characteristics table; deleted ε from the tW1L specification in the Electrical Characteristics
table; applied note 13 to the tW0L specification in the Electrical Characteristics table;
changed RTC accuracy specification in the Electrical Characteristics table from numbers
to graph; added more details to Electrical Characteristics table notes 4, 13, and 14;
revised the last sentence of the Parasite Power section for more clarity; added paragraph
on validation certificates to Detailed Description section; added more details on the
Device Samples Counter in the Other Indicators section
1–5, 11, 24
5 3/13 Corrected a typo of "12" to "192" in the 16-bit decimal column of Table 3 19
6 6/13
Removed the UL 913 5th Ed. compliance statement from the Common iButton Can
Features section and iButton Can Physical Specification table; reworded the Electrical
Characteristics table Note 19
1, 4, 5
7 11/13 Added the Busy state during Copy Scratchpad to the Command-Specific 1-Wire
Communication Protocol—Legend and 1-Wire Communication Examples sections 45, 46
8 3/15 Updated Benefits and Features and Common iButton Can Features sections 1, 55
