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DS1923-F5
Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
DS1923
Hygrochron Temperature/Humidity Logger
iButton with 8kB Data Log Memory
SPECIAL FEATURES Digital Hygrometer Measures Humidity with 8-Bit
(0.6%RH) or 12-Bit (0.04%RH) Resolution Operating Range: -20 to +85°C; 0 to 100%RH
(see Safe Operating Range) Automatically Wakes Up, Measures Temperature
and/or Humidity and Stores Values in 8kB of Datalog Memory in 8- or 16-Bit Format Digital Thermometer Measures Temperature with 8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution Temperature Accuracy Better than ±0.5°C from -10°C to +65°C with Software Correction Built-in Humidity Sensor for Simultaneous Temperature and Humidity Logging Capacitive Polymer Humidity-Sensing Element Hydrophobic Filter Protects Sensor Against Dust,
Dirt, Water, and Contaminants Sampling Rate from 1s up to 273hrs Programmable Recording Start Delay After Elapsed Time or Upon a Temperature Alarm Trip
Point Programmable High and Low Trip Points for
Temperature and Humidity Alarms Quick Access to Alarmed Devices Through
1-Wire� Conditional Search Function 512 Bytes of General-Purpose Memory Plus 64 Bytes of Calibration Memory Two-Level Password Protection of All Memory and Configuration Registers Communicates to Host with a Single Digital Signal at Up to 15.4kbps at Standard Speed or Up to
125kbps in Overdrive Mode Using 1-Wire Protocol Individually Calibrated in a NIST-Traceable
Chamber Calibration Coefficients for Temperature and
Humidity Factory Programmed into Nonvolatile (NV) Memory
APPLICATIONS Temperature and Humidity Logging in Food Preparation and Processing Transportation of Temperature- and Humidity- Sensitive Goods, Industrial Production Warehouse Monitoring Environmental Studies/Monitoring
ORDERING INFORMATION
iButton DESCRIPTION The DS1923 temperature/humidity logger iButton 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 readings taken at equidistant intervals ranging from 1s to 273hrs can be stored. In addition to
this, there are 512 bytes of SRAM for storing application-specific information and 64 bytes for
calibration data. A mission to collect data can be programmed to begin immediately, or after a user-
defined delay or after a temperature alarm. Access to the memory and control functions can be password-
protected. The DS1923 is configured and communicates with a host-computing device through
the serial 1-Wire protocol, which requires only a single data lead and a ground return. Every DS1923 is
factory-lasered with a guaranteed unique 64-bit registration number that allows for absolute
traceability. The durable stainless-steel package 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.
F5 MICROCAN
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data log Memory
DS1923 ABSOLUTE MAXIMUM RATINGS IO Voltage to GND -0.3V, +6V IO Sink current 20mA
Operating Temperature and Humidity Range -20°C to +85°C, 0%RH to 100%RH (See Safe Operating Range Chart)
Storage Temperature and Humidity Range -40°C to +85°C, 0%RH to 100%RH (See Safe Operating Range Chart) This is a stress rating only and functional operation of the device at these or any other conditions above those
indicated in the operation sections of this specification is not implied. Exposure to absolute maximum rating conditions for extended periods of time may affect reliability.
DS1923 ELECTRICAL CHARACTERISTICS (VPUP = 3.0V to 5.25V, TA = -20°C to +85°C)
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
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 found in the DS2480B may be required.
Note 3: Capacitance on the data pin could be 800pF when VPUP is first applied. If a 2.2k� resistor 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, VTH are a function of the internal supply voltage.
Note 5: Voltage below which, during a falling edge on IO, a logic '0' is detected.
Note 6: The voltage on IO needs to be less 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 has to 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 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: � represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH.
Note 14: � 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
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
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: http://www.ibutton.com.
Note 19: WARNING: Not for use as the sole method of measuring or tracking temperature and/or humidity in products and articles that
could affect the health or safety of persons, plants, animals, or other living organisms, including but not limited to foods,
beverages, pharmaceuticals, medications, blood and blood products, organs, flammable, and combustible products. User shall
assure that redundant (or other primary) methods of testing and determining the handling methods, quality, and fitness of the
articles and products should be implemented. Temperature and/or humidity tracking with this product, where the health or safety
of the aforementioned persons or things could be adversely affected, is only recommended when supplemental or redundant
information sources are used. Data logger products are 100% tested and calibrated at time of manufacture by Dallas
Semiconductor/Maxim to ensure that they meet all data sheet parameters, including temperature accuracy. User shall be
responsible for proper use and storage of this product. As with any sensor-based product, user shall also be responsible for
occasionally rechecking the temperature accuracy of the product to ensure it is still operating properly.
Note 20: Response time is determined by measuring the 1/e point as the device transitions from 40 to 90%RH or 90 to 40%RH, whichever
is slower. Test was performed at 5L/min airflow.
Note 21: All DS1923 humidity measurements are 12-bit readings. Missioning determines 8-bit or 16-bit data logging. Battery lifetime is the
same no matter what RH resolution is logged.
Note 22: 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 23: Software corrected accuracy is accomplished using the method detailed in the Software Correction Algorithm for Temperature
section of this data sheet.
Note 24: Every DS1923 Device is measured and calibrated in a controlled, NIST-traceable RH environment.
Note 25: Higher accuracy versions may be available. Contact the factory for details.
Note 26: If this device is exposed to a high humidity environment (>70%RH), and then exposed to a lower RH environment, the device will
read high for a period of time. The device will typically read within +0.5%RH at 20%RH, 30 minutes after being exposed to
continuous 80%RH for 30 minutes.
Note 27: 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 of this data sheet.
Note 28: Individual RH readings always include a noise component (repeatability). To minimize measurement error, average as many
samples as is reasonable.
Note 29: 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 Safe Operating Range chart). For maximum long-term stability, the sensor should not be
exposed or subjected to organic solvents, corrosive agents (strong acids, SO2, H2SO4, CI2 ,HCL, H2S, etc.) and strong bases
(compounds with 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 tolerance to chemicals visit:
http://content.honeywell.com/sensing/prodinfo/humiditymoisture/technical/c15_144.pdf
Note 30: All humidity specifications are determined at +25°C except where specifically indicated. 1) Intentional change, longer recovery time requirement due to modified 1-Wire front end.
PHYSICAL SPECIFICATION Size See mechanical drawing
Weight Ca. 5.0 grams Safety Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus,
approval under Entity Concept for use in Class I, Division 1, Group A, B, C, and D Locations (application
pending)
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Safe Operating Range
DS1923 Temperature Accuracy
NOTE: The graphs are based on 11-bit data. DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Slow Sampling Temperature Only DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Fast Sampling Temperature Only DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Lifetime vs. Temperature, Slow Sampling, Temperature with Humidity
Minimum Lifetime vs. Temperature, Fast Sampling, Temperature with Humidity DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Minimum Product Lifetime vs. Sample Rate (Temperature Only)
NOTE: With humidity logging activated, the lifetime is reduced by less than 11% for sample rate of 3 minutes and slower and by a maximum of 20% for sample rate of 1 minute and faster.
NOTE: With humidity logging activated, the lifetime is reduced by a maximum of 4%. The incremental energy
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
COMMON iButton FEATURES Digital Identification and Information by Momentary Contact Unique Factory-Lasered 64-Bit Registration Number Assures 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 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 Meets UL#913 (4th Edit.); Intrinsically Safe Apparatus: Approved Under Entity Concept for use in Class I,
Division 1, Group A, B, C, and D Locations (Application Pending)
EXAMPLES OF ACCESSORIES
DS9096P Self-Stick Adhesive Pad
DS9101 Multipurpose Clip DS9093RA Mounting Lock Ring
DS9093A Snap-In Fob DS9092 iButton Probe
APPLICATION
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 climatic 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. 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- or equipment-specific data files.
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: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 512-byte general-purpose SRAM, 4) two 256-bit register pages of timekeeping, control, status, and counter registers and
passwords, 5) 64 bytes of calibration memory, and 6) 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 memory, counter registers and several other registers are read-only for the user. Both register pages are write-protected while the device is programmed for a mission. The password registers, one for a read password and another one for a
read/write password can only be written to but never read.
The hierarchical structure of the 1-Wire protocol is shown in Figure 2. The bus master must first provide one of the
eight ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5) Skip ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM, or 8) Resume. Upon completion of an Overdrive ROM command byte 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 executed, 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 significant bit first.
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 1. DS1923 BLOCK DIAGRAM
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered 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 conserved, and 2) if the
battery is exhausted for any reason, the ROM may still be read.
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 CRC of the first 56 bits. See Figure 4 for details. The 1-
Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 3. The polynomial is X8 + X5 + X4 + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy
Check is available in Dallas Application Note 27.
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, then the serial number followed by the
temperature range code is entered. After the range code 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: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 2. HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL
Figure 3. 1-Wire CRC GENERATOR
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 4. 64-BIT LASERED ROM
MEMORY
The memory map of the DS1923 is shown in Figure 5. The 512 bytes general-purpose SRAM are located in pages
0 through 15. The various registers to set up and control the device fill page 16 and 17, called Register Pages 1 and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. The "data log" logging
memory starts at address 1000h (page 128) and extends over 256 pages. The memory pages 20 to 127 are reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the
SRAM memory or the register page. The data memory can be written at any time. 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 recommended. See the Security by Password section for ways to protect the memory. The access type for the 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 supervision 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 and the calibration memory. See the Address Register and Transfer Status section for details.
Figure 5. DS1923 MEMORY MAP
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 6. DS1923 REGISTER PAGES MAP
Note: The first entry in column ACCESS TYPE is valid between missions. The second entry shows the applicable
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TIMEKEEPING AND CALENDAR
The real-time clock/alarm and calendar information is accessed by reading/writing the appropriate bytes in the register page, address 200h to 205h. For readings to be valid, all RTC registers must be read sequentially starting
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 real-time clock registers is BCD format (Binary-Coded Decimal).
Real-Time Clock and RTC Alarm Register Bitmap
The real-time clock of the DS1923 can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register (address 202h) is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour
mode, bit 5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20 to 23 hours). 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 compensate for leap years. For every year value that is either 00 or a multiple of 4 the device will add a 29th of February. This will work 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 temperature/humidity logging events. The sample rate can be any value from 1 to 16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging
events is 1 second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and the longest time is 273.05 hours (sample rate = 3FFFh). The EHSS bit is located in the RTC Control Register at
address 0212h. It is important that the user sets the EHSS bit accordingly while setting the Sample Rate register. A sample rate of 0000h is not valid and must be avoided under all circumstances. This causes the device to
enter into an unrecoverable state.
Sample Rate Register Bitmap
During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be
written to 1.
TEMPERATURE CONVERSION
The DS1923 measures temperatures in the range of -20°C to +85°C. Temperature values are represented as a 8-
or 16-bit unsigned binary number with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.
The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte TRL are valid. The five lower bits all read zero. 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.
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Temperature Conversion Result Register Bitmap TRL TRH
With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is calculated as
�(°C) = TRH/2 - 41 + TRL/512 (16-bit mode, TLFS = 1, see address 0213h)
�(°C) = TRH/2 - 41 (8-bit mode, TLFS = 0, see address 0213h) This equation is valid for converting temperature readings 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 equation above needs to be resolved to
TALM = 2 * � (°C) + 82
Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C. The TALM value needs to be converted into hexadecimal 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- or 16-bit) only the most significant byte of a temperature conversion is used to determine
whether an alarm is generated.
Temperature Conversion Examples
Temperature Alarm Threshold Examples
HUMIDITY CONVERSION
In addition to temperature, the DS1923 can log humidity data in 8-bit or 16-bit format. Humidity values are
represented as 8- 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 whenever a Forced Conversion command is executed (see
Memory/Control Function Commands) or during a mission, if the device is set up to log humidity 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 will 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.
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Latest Humidity Conversion Result Register Bitmap HRL HRH
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.
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) * 0.0307 + 0.958 HALM = ADVAL * 256/5.02
Round HALM to the nearest integer.
The HALM value needs to be converted into hexadecimal before it can be written to one of the humidity alarm
threshold registers (Low Alarm address 020Ah; High Alarm address 020B). Independent of the conversion mode (8-or 16-bit) only the most significant byte of a humidity conversion is used to determine whether an alarm
will be generated. The alarm thresholds are applied to the raw humidity readings. Therefore, if software correction is used, the effect of the software correction is to be reversed before calculating a humidity alarm threshold.
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. Humidity Conversion Examples
Humidity Alarm Threshold Examples
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
TEMPERATURE SENSOR ALARM
The DS1923 has two Temperature Alarm Threshold registers (address 0208h, 0209h) to store values, which 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.
Temperature Sensor Control Register Bitmap
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.
Register Details
HUMIDITY ALARM
The DS1923 has two Humidity Alarm Threshold registers (address 020Ah, 020Bh) to store values, which
determine 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.
Humidity Sensor Control Register Bitmap
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.
Register Details
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
REAL-TIME CLOCK CONTROL
To minimize the power consumption of a DS1923, the real-time clock oscillator should be turned off when 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 specified in seconds or minutes.
RTC Control Register Bitmap
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.
Register Details
MISSION CONTROL
The DS1923 is set up for its operation by writing appropriate 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) is to be used and whether old data can be overwritten by new data, once the data log memory is full. An additional control bit can be set to tell the DS1923 to wait with logging data
until a temperature alarm is encountered.
Mission Control Register Bitmap
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.
Register Details
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 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 iButtons the devices that encountered an alarm can quickly be identified by means of the Conditional Search
command (see ROM Function Commands). The humidity and temperature alarm only occurs if enabled (see Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled. Alarm Status Register Bitmap
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 function is invoked. See Memory and Control Functions for
details.
Register Details
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
GENERAL STATUS
The information in the general status register tells the host computer whether a mission-related command was executed successfully. Individual status bits indicate whether the DS1923 is performing a mission, waiting for a
temperature alarm to trigger the logging of data or whether the data from the latest mission has been cleared.
General Status Register Bitmap
There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.
Register Details
MISSION START DELAY
The content of the Mission Start Delay Counter tells how many minutes have to expire from the time a mission was
started until the first measurement of the mission will take place (SUTA = 0) or until the device will start testing the temperature for a temperature alarm (SUTA = 1). The Mission Start Delay is stored as an unsigned 24-bit integer
number. The maximum delay is 16777215 minutes, equivalent to 11650 days or roughly 31 years. If the start delay is non-zero and the SUTA bit is set to 1, first the delay has to expire before the device starts testing for temperature
alarms to begin logging data.
Mission Start Delay Counter
During a mission, there is only read access to these registers. For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1923 to store all readings
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.
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
MISSION TIME STAMP
The Mission Time Stamp indicates the date and time of the first temperature and/or humidity sample of the mission. There is only read access to the Mission Time Stamp Register.
Mission Time Stamp Registers Bitmap
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 Sample Counter together with the starting address and the logging format (8 or
16 bits) provides the information to identify valid blocks of data that have been gathered during the current (MIP = 1) or latest mission (MIP = 0). See section Data log Memory Usage for an illustration. Note that when SUTA = 1,
the Mission Sample Counter does not increment when the first sample is logged. Mission Sample Counter Register Map
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 Sample Counter and Device Sample
Counter.
The number read from the Mission Sample Counter indicates how often the DS1923 woke up during a mission to measure temperature and/or humidity. The number format is 24-bit unsigned integer. The Mission Sample Counter
is reset through the Clear Memory command.
OTHER INDICATORS
The Device Sample Counter is similar to the Mission Sample Counter. 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 SUTA mode. Between missions the counter increments whenever the Forced Conversion command is executed.
This way the Device Sample Counter functions like a gas gauge for the battery that powers the iButton.
Device Sample Counter Register Map
There is only read access to this register. The Device Sample Counter is reset to zero when the iButton is assembled. The counter increments a couple of
times during final test. The number format is 24-bit unsigned integer. The maximum number that can be represented in this format is 16777215.
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Device Configuration Byte DS2422 DS1923 DS1922L DS1922T
There is only read access to this register.
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 needs to be transmitted right after the command code of the memory or control function. If password checking is enabled the
password transmitted is compared to the passwords stored in the device. The data pattern stored in the Password Control register determines whether password checking is enabled.
Password Control Register
During a mission, there is only read access to this register.
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 will be 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. Before enabling password checking, passwords for read-only access as well as for full access (read/write/control)
need to be written to the password registers. Setting up a password or enabling/disabling 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 redefined at the same time. Read Access Password Register
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress. The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1… RP62, RP63. This
password only applies to the function “Read Memory with CRC”. The DS1923 delivers the requested data only if
the password transmitted by the master was correct or if password checking is not enabled. Full-Access Password Register
There is only write access to this register. Attempting to read the password will report all zeros. The password
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It affects the functions “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 scratchpad to its memory
location, erase the scratchpad by filling it with new data (write scratchpad command). Otherwise a copy of the passwords will remain in the scratchpad for public read access.
DATA LOG MEMORY USAGE
Once setup for a mission, the DS1923 logs the temperature measurements and/or humidity at equidistant time points entry after entry in its data log memory. The data log memory is able to store 8192 entries in 8-bit format or
4096 entries in 16-bit format (Figure 7A). If temperature as well as humidity is 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 different 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 Time Stamp) and the interval between temperature measurements one
can reconstruct 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 further recording (disable “rollover”) or overwrite the previously recorded
data (enable “rollover”), one entry at a time, starting again at the beginning of the respective memory section. The contents of the Mission Sample Counter in conjunction with the sample rate and the Mission Time Stamp then
allows 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.
Figure 7A. ONE CHANNEL LOGGING
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
Figure 7B. TWO CHANNEL LOGGING, EQUAL RESOLUTION
Figure 7C. TWO CHANNEL LOGGING, DIFFERENT RESOLUTION
MISSIONING
The typical task of the DS1923 iButton 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 of all, DS1923 needs to have its real-time clock set to valid time and date. This reference time may be the
local time, or, when used inside of a mobile unit, UTC (also called GMT, Greenwich Mean Time) or any other time standard that was agreed upon. The real-time clock oscillator must be running (EOSC = 1). The memory assigned to store the Mission Time Stamp, Mission Sample Counter, and Alarm Flags must be cleared using the Memory
Clear 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 have to be made in any case, regardless of the type of object to be monitored 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.
How to convert a temperature value into the binary code to be written to the threshold registers is described under
DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory
and/or high-threshold. This will make the device respond to a Conditional Search command (see ROM Function Commands), provided that an alarming condition 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 (single 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 estimated duration of a mission is 10 days (= 14400 minutes), for example,
then the 8192-byte capacity of the data log memory would be sufficient to store a new 8-bit value every 1.8 minutes (110 seconds). 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 needs to be written to the Sample Rate Register. The sample rate may be any value from 1 to 16383, coded as an unsigned 14-bit binary number. A
sample rate of all zeros is not valid and must be avoided under all circumstances. This causes the device to enter into an unrecoverable state. The fastest sample rate is one sample per second (EHSS = 1, Sample Rate =
0001h) and the slowest is one sample every 273.05 hours (EHSS = 0, Sample Rate = 3FFFh). To get one sample every 6 minutes, for example, the sample rate value needs to 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 needs to be enabled. See Security by Password for more details. The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command,
the DS1923 sets the MIP flag and clear 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 time stamp register, and logs the first entry of the mission. This increments both the Mission Sample Counter and Device Sample 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 waist until the start delay is over. Then the device wakes up in intervals as specified by the sample
rate and EHSS bit and measure the temperature. This increments the Device Sample Counter only. The first sample of the mission is logged when the temperature alarm occurred. However, the Mission Sample Counter will
not increment. One sample period later the Mission Time Stamp is set. From then on, both the Mission Sample Counter and Device Sample Counter increment at the same time. All subsequent log entries will be 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 memory of the DS1923 can be read at any time, e. g., to watch the progress of a mission. Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.
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 will be written or from which
data will be sent to the master upon a Read command. Register E/S acts like a byte counter and transfer 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 Register 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
