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DS1923-F5#
iButton Hygrochron Temperature/Humidity Logger with 8KB Data-Log Memory
DS1923iButton Hygrochron
Temperature/Humidity Logger
with 8KB Datalog Memory
General DescriptionThe 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.
ApplicationsTemperature 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 FeaturesHigh Accuracy, Full-Featured Digital Temperature and
Humidity Logger Simplifies Temperature Data
Collection and Dissemination of Electronic
Temperature RecordDigital Hygrometer Measures Humidity with 8-Bit
(0.6%RH) or 12-Bit (0.04%RH) ResolutionTemperature Accuracy Better Than ±0.5°C from
-10°C to +65°C with Software CorrectionMeasures Temperature with 8-Bit (0.5°C) or 11-Bit
(0.0625°C) ResolutionOperating Range: -20°C to +85°C; 0 to 100%RH
(see Safe Operating RangeGraph)Automatically Wakes Up, Measures Temperature
and/or Humidity, and Stores Values in 8kB of
Data-Log Memory in 8-Bit or 16-Bit FormatBuilt-In Capacitive Polymer Humidity Sensor for
Humidity LoggingSampling Rate from 1s Up to 273hrProgrammable High and Low Trip Points forProgrammable Recording Start Delay After Elapsed
Time or Upon a Temperature Alarm Trip Point512 Bytes of General-Purpose Memory Plus
64 Bytes of Calibration MemoryTwo-Level Password Protection of All Memory and
Configuration RegistersIndividually Calibrated in a NIST-Traceable ChamberCalibration Coefficients for Temperature and
Humidity Factory Programmed Into Nonvolatile (NV)
Memory
Rugged Construction Survives Harsh EnvironmentsHydrophobic Filter Protects Sensor Against Dust,
Dirt, Contaminants, and Water Droplets/
Condensation with IP56 Enclosure RatingCE, FCC, and UL913 Certifications
Simple Serial Port Interfaces to Most Microcontrollers
for Rapid Data TransferCommunicates to Host with a Single Digital Signal
Up to 15.4kbps at Standard Speed or Up to
125kbps in Overdrive Mode Using 1-Wire ProtocolQuick Access to Alarmed Devices Through 1-Wire
Conditional Search Function
Ordering Information
Common iButton Can Featuresand Pin Configurationappear
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
PARTACCESSORYDS9096P Self-Stick Adhesive Pad
DS9101 Multipurpose Clip
DS9093RA Mounting Lock Ring
DS9093A Snap-In FOB
DS9092 iButton Probe
PARTTEMP RANGEPIN-PACKAGEDS1923-F5# -20°C to +85°C F5 Can
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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*
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITS
IO PIN: GENERAL DATA1-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 CYCLEStandard 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
7μs
Standard speed, VPUP > 4.5V 1.5 5
Standard speed 1.5 8Presence-Detect Fall Time
(Note 12) tFPD
Overdrive speed 0.15 1
μs
*See the Safe Operating Rangegraph.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Electrical Characteristics (continued)(VPUP= +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSStandard 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)
728μs
Standard speed, VPUP > 4.5V 65 75
Standard speed 71.5 75Presence-Detect Sample Time
(Note 1) tMSP
Overdrive speed 8 9
μs
IO PIN: 1-Wire WRITEStandard speed 60 120
Overdrive speed, VPUP > 4.5V (Note 11) 6
12Write-Zero Low Time
(Notes 1, 13) tW0L
Overdrive speed (Note 11)
7.5 12μs
Standard speed 5 15 Write-One Low Time
(Notes 1, 13) tW1L Overdrive speed 1 1.95 μs
IO PIN: 1-Wire READStandard 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 CONVERTER8-bit mode (Note 15) 30 75 Conversion Time tCONV16-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) 0.640.040.04%RH
RH Range (Note 23) 0 100 %RH
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Electrical Characteristics (continued)(VPUP= +3.0V to +5.25V, TA= -20°C to +85°C.) (Note 31)
PARAMETERSYMBOLCONDITIONSMINTYPMAXUNITSRH 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 VPUPis first applied. If a 2.2kΩresistor is used to pull up the data line,
2.5μs after VPUPhas been applied, the parasite capacitance does not affect normal communications.
Note 4:VTLand VTHare functions of the internal supply voltage, which is a function of VPUPand the 1-Wire recovery times. The
VTHand VTLmaximum 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 VILMAXwhenever 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 VTHis crossed during a rising edge on IO, the voltage on IO must drop by VHYto 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 tREHafter VTHhas been previously reached.
Note 11:Numbers in boldare notin 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 VPUPand 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 VILto 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 VILto 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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
Temperaturesection.
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 Compensationsection.
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 Rangegraph). 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 VALUESDS1923 VALUES
STANDARD SPEED
(μs)
OVERDRIVE SPEED
(μs)
STANDARD SPEED
(μs)
OVERDRIVE SPEED
(μs) PARAMETER
MINMAXMINMAXMINMAXMINMAX tSLOT (including tREC)61 (undefined) 7 (undefined) 65* (undefined)
9.5 (undefined)
tRSTL 480 (undefined) 48 80
690 720
7080
tPDH 15 60 2 6 15
63.5 2
7tPDL 60 240 8 24 60
287728tW0L 60 120 6 16 60 120
7.512*Intentional change; longer recovery time requirement due to modified 1-Wire front-end.
Note:Numbers in boldare notin 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)
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Safe Operating RangeHUMIDITY (
RH)
SAFE OPERATING ZONE
STORAGE
ONLY
TEMPERATURE (°C)
Temperature AccuracyNOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.
TEMPERATURE (°C)
ERROR (UNCORRECTED MAXIMUM ERROR
UNCORRECTED MINIMUM ERROR
SW CORRECTED MAXIMUM ERROR
SW CORRECTED MINIMUM ERROR
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Minimum Lifetime vs. Temperature, Slow Sampling (Temperature Only) MI
NIMUM P
ODUC
LI
MI
NIMUM P
ODUC
LI
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
TEMPERATURE (°C)
TEMPERATURE (°C)
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Minimum Lifetime vs. Temperature, Fast Sampling (Temperature Only)INIMUM P
ODUC
LI
INIMUM P
ODUC
LI
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
TEMPERATURE (°C)
TEMPERATURE (°C)
100
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
TE
PERA
TURE PL
IDI
MI
NIMUM
PRODUCT LIFETIME (YEARS)
EVERY MINUTE
EVERY 60 MINUTESNO SAMPLES
EVERY 3 MINUTES
OSCILLATOR OFF
EVERY 10 MINUTES
TEMPERATURE (°C)
Minimum Lifetime vs. Temperature, Slow Sampling
(Temperature with Humidity) TE
PERA
TURE PL
IDI
MI
NIMUM
PRODUCT LIFETIME (DA
YS)
EVERY SECOND
EVERY 30 SECONDS
EVERY 3 SECONDS
EVERY 60 SECONDS
EVERY 10 SECONDS
TEMPERATURE (°C)
Minimum Lifetime vs. Temperature, Fast Sampling
Temperature with Humidity)
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Minimum Product Lifetime vs. Sample Rate (Temperature Only)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
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
IT M
INIMUM PR
T L
IFE
(Y
11-B
IT M
INIMUM PR
T L
IFE
(Y
0.1
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
RTC Accuracy (Typical)DRIFT (MINUTES/MONTH)
TEMPERATURE (°C)
Detailed DescriptionThe 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.
OverviewThe 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
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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
THERMAL
SENSEADC1
DATA-LOG MEMORY
8KB
INTERNAL
TIMEKEEPING,
CONTROL REGISTERS,
AND COUNTERS
ROM
FUNCTION
CONTROL
1-Wire PORTPARASITE-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 PowerThe 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, andif 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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 NETOTHER DEVICES
DS1923
Figure 2. Hierarchical Structure for 1-Wire Protocol
MSB
8-BIT
CRC CODE48-BIT SERIAL NUMBER
MSBMSBLSB
LSB
LSB
8-BIT FAMILY CODE
(41h)
MSBLSB
Figure 3. 64-Bit Lasered ROM
64-Bit Lasered ROMEach 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
MemoryFigure 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 Algorithmsections 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 Passwordsection 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
STAGE0X1X2X3X4
POLYNOMIAL = X8 + X5 + X4 + 1
INPUT DATA5X6X7X8
Figure 4. 1-Wire CRC Generator
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
ADDRESSBIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0FUNCTIONACCESS*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
Statussection for details.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
ADDRESSBIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0FUNCTIONACCESS*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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Detailed Register Descriptions
Timekeeping and CalendarThe 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 RateThe 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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00206h Sample Rate Low
0207h 0 0 Sample Rate High
RTC Registers Bitmap
ADDRESSBIT 7BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00200h 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Latest Temperature Conversion Result Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0BYTE020Ch T2 T1 T0 0 0 0 0 0 TRL
020Dh T10 T9 T8 T7 T6 T5 T4 T3 TRH
Temperature ConversionThe 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 ConversionIn 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 Commandssection)
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
TRHTRLMODEHEX DECIMALHEXDECIMAL(°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)
HEXDECIMAL25.5 85h 133
-10.0 3Eh 62
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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.
ADDRESSBIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 0 BYTE020Eh H3 H2 H1 H0 X X X X
HRL 020Fh H11 H10 H9 H8 H7 H6 H5 H4
HRH
16-BIT MODE, HLFS = 18-BIT MODE, HLFS = 0IVAL = (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
HRHHRLMODEHEXDECIMALHEXDECIMALHUMIDITY (%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
4834.70
Table 4. Humidity Alarm Threshold Examples
HALMHUMIDITY (%RH)HEXDECIMAL 97h 151
58h 88
Latest Humidity Conversion Result Register BitmapThe result is a raw humidity reading that needs to be
corrected to achieve the specified accuracy. See the
Software Correction Algorithm for Humiditysection 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Temperature Sensor AlarmThe 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). Thisbit 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 AlarmThe 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 ControlTo 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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00210h 0 0 0 0 0 0 ETHA ETLA
RTC Control Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00212h 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
ADDRESSBIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Bit 0: Enable Oscillator (EOSC). This bit controls thecrystal 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
logic1.
Mission ControlThe 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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00213h 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Alarm StatusThe 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 Alarmand Humidity Alarmsections). 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
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 StatusThe 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, thedevice 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]
Alarm Status Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00214h BOR 1 1 1 HHF HLF THF TLF
General Status Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00215h 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 Commandssection for details.
Note:There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Mission Samples Counter Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00220h Low Byte
0221h Center Byte
0222h High Byte
Mission Timestamp Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00219h 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 DelayThe 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 TimestampThe 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 IndicatorDepending 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 Usagesection 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
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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00216h Delay Low Byte
0217h Delay Center Byte
0218h Delay High Byte
Note:During a mission, there is only read access to this register.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Other IndicatorsThe 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 Bitmaptable shows the codes
assigned to the various devices.
Security by PasswordThe 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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00223h Low Byte
0224h Center Byte
0225h High Byte
Password Control Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00227h EPW
Device Configuration Register Bitmap
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0PART0 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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
ADDRESSBIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 00228h 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
ADDRESSBIT 7BIT 6BIT 5BIT 4BIT 3BIT 2BIT 1BIT 00230h 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
Data-Log Memory UsageOnce 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.
MissioningThe 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 Conversionsection 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 the1-WireROM 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.
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
8-BIT ENTRIES
TEMPERATURE
HUMIDITY DATA
ETL = 1; EHL = 0 OR ETL = 0; EHL = 1
TLFS = HLFS = 0
1000h
2FFFh
16-BIT ENTRIES
TEMPERATURE
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
8-BIT ENTRIES
ETL = EHL = 1
TLFS = HLFS = 0
1000h
1FFFh
HUMIDITY DATA
8-BIT ENTRIES
2000h
2FFFh
TEMPERATURE
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
16-BIT ENTRIES
2000h
2FFFh
Figure 7b. 2-Channel Logging, Equal Resolution
TEMPERATURE
8-BIT ENTRIES
ETL = EHL = 1
TLFS = 0; HLFS = 1
1000h
19FFh
HUMIDITY DATA
16-BIT ENTRIES
1A00h
2DFFh
TEMPERATURE
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
8-BIT ENTRIES
2400h
2DFFh
(NOT USED)(NOT USED)
2E00h
2FFFh
2E00h
2FFFh
Figure 7c. 2-Channel Logging, Different Resolution
DS1923iButton Hygrochronemperature/Humidity Logger
with8KB Datalog Memory
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 StatusBecause 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 5of 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 NUMBER76543210TARGET 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
