DS1923

DS1923 DALLAS | Alldatasheet

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1 of 52 REV: 110504 DS1923 Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory www.maxim-ic.com SPECIAL FEATURES /g167/g32Digital Hygrometer Measures Humidity with 8-Bit (0.6%RH) or 12-Bit (0.04%RH) Resolution /g167/g32Operating Range: -20 to +85°C; 0 to 100%RH (see Safe Operating Range) /g167/g32Automatically Wakes Up, Measures Temperature and/or Humidity and Stores Values in 8kB of Datalog Memory in 8- or 16-Bit Format /g167/g32Digital Thermometer Measures Temperature with 8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution /g167/g32Temperature Accuracy Better than ±0.5°C from -10°C to +65°C with Software Correction /g167/g32Built-in Humidity Sensor for Simultaneous Temperature and Humidity Logging /g167/g32Capacitive Polymer Humidity-Sensing Element /g167/g32Hydrophobic Filter Protects Sensor Against Dust, Dirt, Water, and Contaminants /g167/g32Sampling Rate from 1s up to 273hrs /g167/g32Programmable Recording Start Delay After Elapsed Time or Upon a Temperature Alarm Trip Point /g167/g32Programmable High and Low Trip Points for Temperature and Humidity Alarms /g167/g32Quick Access to Alarmed Devices Through 1-Wire /g210 Conditional Search Function /g167/g32512 Bytes of General-Purpose Memory Plus 64 Bytes of Calibration Memory /g167/g32Two-Level Password Protection of All Memory and Configuration Registers /g167/g32Communicates 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 /g167/g32Individually Calibrated in a NIST-Traceable Chamber /g167/g32Calibration Coefficients for Temperature and Humidity Factory Programmed into Nonvolatile (NV) Memory

APPLICATIONS

/g167/g32Temperature and Humidity Logging in Food Preparation and Processing /g167/g32Transportation of Temperature- and Humidity- Sensitive Goods, Industrial Production /g167/g32Warehouse Monitoring /g167/g32Environmental Studies/Monitoring

ORDERING INFORMATION

DS1923-F5 -20°C to +85°C F5 iButton iButton DESCRIPTION The DS1923 temperature/humidity logger i Button 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 IO GND 0.51 5.89 16.25 17.35 /g226 Front Side Brand A1 41 000000FBC52B 1-Wire /g226 /g226 /g226 Hygrochron TM Back Side Brand All dimensions are shown in millimeters. 1-Wire and iButton are registered trademarks of Dallas Semiconductor. Hygrochron is a trademark of Dallas Semiconductor.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data log Memory 2 of 52 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) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS IO Pin General Data 1-Wire Pullup Resistance RPUP (Notes 1, 2) 2.2 k/g87 Input Capacitance C IO (Note 3) 100 800 pF Input Load Current I L IO pin at VPUP 6 10 µA High-to-Low Switching Threshold VTL (Notes 4. 5) 0.4 3.2 V Input Low Voltage V IL (Notes 1, 6) 0.3 V Low-to-High Switching Threshold VTH (Notes 4, 7) 0.7 3.4 V Switching Hysteresis V HY (Note 8) 0.09 N/A V Output Low Voltage V OL At 4mA (Note 9) 0.4 V Standard speed, RPUP = 2.2k/g87 5 Overdrive speed, RPUP = 2.2k/g87 2 Recovery Time (Note 1) tREC Overdrive speed, directly prior to reset pulse; RPUP = 2.2k/g87 5 µs Rising-Edge Hold-off Time tREH (Note 10) 0.6 2.0 µs Standard speed 65 Overdrive speed, VPUP > 4.5V 8 Timeslot Duration (Note 1) tSLOT Overdrive speed (Note 11) 9.5 µs IO Pin, 1-Wire Reset, Presence Detect Cycle Standard speed, VPUP > 4.5V 480 720 Standard speed (Note 11) 690 720 Overdrive speed, VPUP > 4.5V 48 80 Reset Low Time (Note 1) tRSTL Overdrive speed (Note 11) 70 80 µs Standard speed, VPUP > 4.5V 15 60 Standard speed (Note 11) 15 63.5 Presence-Detect High Time tPDH Overdrive speed (Note 11) 2 7 µs Standard speed, VPUP > 4.5V 1.5 5 Standard speed 1.5 8 Presence-Detect Fall Time (Note 12) tFPD Overdrive speed 0.15 1 µs Standard speed, VPUP > 4.5V 60 240 Standard speed (Note 11) 60 287 Overdrive speed, VPUP > 4.5V (Note 11) 7 24 Presence-Detect Low Time t PDL Overdrive speed (Note 11) 7 28 µs Standard speed, VPUP > 4.5V 65 75 Standard speed 71.5 75 Presence-Detect Sample Time (Note 1) t MSP Overdrive speed 8 9 µs

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 3 of 52 PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS IO Pin, 1-Wire Write Standard speed 60 120 Overdrive speed, VPUP > 4.5V (Note 11) 6 12 Write-0 Low Time (Note 1) tW0L Overdrive speed (Note 11) 7.5 12 µs Standard speed 5 15 - /g101 Write-1 Low Time (Notes 1, 13) tW1L Overdrive speed 1 1.95 - /g101µs IO Pin, 1-Wire Read Standard speed 5 15 - /g100 Read Low Time (Notes 1, 14) tRL Overdrive speed 1 1.95 - /g100µs Standard speed tRL + /g100 15 Read Sample Time (Notes 1, 14) tMSR Overdrive speed tRL + /g100 1.95 µs Real-Time Clock Accuracy +25°C -3 +3 min./ month Frequency Deviation /g68F -20°C to +85°C -300 +60 PPM Temperature Converter 8-bit mode (Note 15) 30 75 Conversion Time t CONV 16-bit mode (11 bits) 240 600 ms Thermal Response Time Constant /g116RESP iButton package (Note 16) 130 s Conversion Error Without Software Correction /g68/g74 (Notes 15, 17, 18, 19) See Temperature Accuracy Graphs °C Conversion Error With Software Correction /g68/g74 (Notes 15, 17, 18, 19) See Temperature Accuracy Graphs °C Humidity Converter (Note 30) Humidity Response Time Constant /g116RH Slow moving air (Note 20) 30 s (Note 21) 8 12 12 bits RH Resolution 0.64 0.04 0.04 %RH RH Range (Note 22) 0 100 %RH RH Accuracy and Interchangeability With software correction (Notes 18, 19, 23, 24, 25) ±5 %RH RH Nonlinearity With software correction (Note 18) <1 RH Hysteresis (Notes 26, 27) 0.5 %RH RH Repeatability (Note 28) ±0.5 %RH Long-Term Stability At 50%RH (Note 29) <1.0 %RH/y 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/g87 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 11: Highlighted numbers are NOT in compliance with the published iButton standards. See comparison table below. 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: /g101 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. Note 14: /g100 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input high threshold of the bus master. 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 of 2000.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 4 of 52 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, SO 2, 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. Standard Values DS1923 Values Parameter Standard Speed Overdrive Speed Standard Speed Overdrive Speed Name Min Max Min Max Min Max Min Max tRSTL 480µs (undef.) 48µs 80µs 690µs 720µs 70µs 80µs tPDH 15µs 60µs 2µs 6µs 15µs 63.5µs 2µs 7µs tPDL 60µs 240µs 8µs 24µs 60µs 287µs 7µs 28µs tW0L 60µs 120µs 6µs 16µs 60µs 120µs 7.5µs 12µs 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 (4 th 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 5 of 52 Safe Operating Range 100 - 4 0 - 2 0 0 2 04 06 08 0 Temperature (°C) Humidity (%RH) Safe Operating Zone Storage Only DS1923 Temperature Accuracy -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 - 2 0 - 1 00 1 02 03 04 05 06 07 08 0 Temperature (°C) DS1923: Error (°C) Uncorrected Max Error Uncorrected Min Error SW Corrected Max Error SW Corrected Min Error NOTE: The graphs are based on 11-bit data.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 6 of 52 Minimum Lifetime vs. Temperature, Slow Sampling Temperature Only - 2 0 - 1 00 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 8-Bit Min. Product Lifetime (years) Every Minute Every 3 Min. Every 10 Min. Every 60 Min. No Samples Osc. Off - 2 0 - 1 0 0 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 11-Bit Min. Product Lifetime (years) Every Minute Every 3 Min. Every 10 Min. Every 30 Min. Every 60 Min. Every 300 Min. No Samples Osc. Off

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 7 of 52 Minimum Lifetime vs. Temperature, Fast Sampling Temperature Only 100 150 200 250 300 350 - 2 0 - 1 0 0 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 8-Bit Min. Product Lifetime (days) Ev ery Second Every 3 Sec. Every 10 Sec. Every 30 Sec. Every 60 Sec. 100 - 2 0 - 1 0 0 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 11-Bit Min. Product Lifetime (days) Every Second Every 3 Sec. Every 10 Sec. Every 30 Sec. Every 60 Sec.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 8 of 52 Minimum Lifetime vs. Temperature, Slow Sampling, Temperature with Humidity - 2 0 - 1 00 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 8-Bit Temp. plus Humidity Min. Product Lifetime (years) Every Minute Every 3 Min. Every 10 Min. Every 60 Min. No Samples Osc. Off Minimum Lifetime vs. Temperature, Fast Sampling, Temperature with Humidity 100 150 200 250 300 350 - 2 0 - 1 0 0 1 02 03 04 05 06 07 08 0 DS1923: Temperature (°C) 8-Bit Temp. plus Humidity Min. Product Lifetime (days) Every Second Every 3 Sec. Ev ery 10 Sec. Every 30 Sec. Every 60 Sec.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 9 of 52 Minimum Product Lifetime vs. Sample Rate (Temperature Only) 0.01 0.1 0.01 0.1 1 10 100 DS1923: Minutes between Samples 8-Bit Min. Product Lifetime (years) 0°C 40°C 60°C 75°C 85°C 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. 0.001 0.01 0.1 0.01 0.1 1 10 100 DS1923: Minutes between Samples 11-Bit Min. Product Lifetime (years) 0°C 40°C 60°C 75°C 85°C 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.

Button website ( www.ibutton.com). memory for storing application- or equipment-specific data files. read/write password can only be written to but never read. Figure 11. After a ROM function command is successfully executed, the memory and control functions become and control function commands is described in Figure 9. All data is read and written least significant bit first.

Figure 6. DS1923 REGISTER PAGES MAP access type while a mission is in progress.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 15 of 52 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0200h 0 10 Seconds Single Seconds 0201h 0 10 Minutes Single Minutes 0202h 0 12/24 20h. AM/PM 10h. Single Hours 0203h 0 0 10 Date Single Date 0204h CENT 0 0 10m. Single Months 0205h 10 Years Single Years 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0206h Sample Rate Low 0207h 0 0 Sample Rate High 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 16 of 52 Latest Temperature Conversion Result Register Bitmap ADDR b7 b6 b5 b4 b3 b2 b1 b0 020Ch T2 T1 T0 0 0 0 0 0 TRL 020Dh T10 T9 T8 T7 T6 T5 T4 T3 TRH With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is calculated as /g74(°C) = TRH/2 - 41 + TRL/512 (16-bit mode, TLFS = 1, see address 0213h) /g74(°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 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 Mode TRH hex decimal TRL hex decimal /g74(°C) 8-bit 54h 84 /g190 /g190 1.0 8-bit 17h 23 /g190 /g190 -29.5 16-bit 54h 84 00h 0 1.000 16-bit 17h 23 60h 96 -29.3125 Temperature Alarm Threshold Examples /g74(°C) TALM hex decimal 25.5 85h 133 -10.0 3Eh 62 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 17 of 52 Latest Humidity Conversion Result Register Bitmap ADDR b7 b6 b5 b4 b3 b2 b1 b0 020Eh H3 H2 H1 H0 X X X X HRL 020Fh H11 H10 H9 H8 H7 H6 H5 H4 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. 16-Bit Mode, HLFS = 1 8-Bit Mode, HLFS = 0 IVAL = (HRH * 256 + HRL)/16 Round IVAL down to the nearest integer; this eli- minates the undefined 4 bits of HRL. (N/A) ADVAL = IVAL*5.02/4096 ADVAL = HRH*5.02/256 HUMIDITY(%RH) = (ADVAL - 0.958)/0.0307 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 Mode HRH hex decimal HRL hex decimal Humidity(%RH) 8-bit B5h 181 /g190 /g190 84.41 8-bit 67h 103 /g190 /g190 34.59 16-bit B5h 181 C0h 12 84.89 16-bit 67h 103 30h 48 34.70 Humidity Alarm Threshold Examples Humidity(%RH) HALM hex decimal 65 97h 151 25 58h 88 These examples do not include the effects of software correction.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 18 of 52 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0210h 0 0 0 0 0 0 ETHA ETLA 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 Bit Description Bit(s) Definition ETLA: Enable Tempera- ture Low Alarm b0 This bit controls whether, during a mission, the Temperature Low Alarm Flag TLF can be set, if a temperature conversion 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. ETHA: Enable Temperature High Alarm b1 This bit controls whether, during a mission, the Temperature High Alarm Flag THF can be set, if a temperature conversion 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. 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0211h 1 1 1 1 1 1 EHHA EHLA 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 Bit Description Bit(s) Definition EHLA: Enable Humidity Low Alarm b0 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. EHHA: Enable Humidity High Alarm b1 This bit controls whether, during a mission, the Humidity High Alarm Flag HHF can be set, if a value from the humidity 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, humidity high alarms are not generated.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 19 of 52 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0212h 0 0 0 0 0 0 EHSS EOSC 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 Bit Description Bit(s) Definition EOSC: Enable Oscillator b0 This bit controls the crystal oscillator of the real-time clock. When set to logic 1, the oscillator starts operation. 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 temperature or humidity conversion must not be attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state. EHSS: Enable High Speed Sample b1 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. 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0213h 1 1 SUTA RO HLFS TLFS EHL ETL 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 Bit Description Bit(s) Definition ETL: Enable Temperature Logging b0 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. EHL: Enable Humidity Logging b1 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 will 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 temperature, typically both, humidity and temperature logging are enabled, i. e., ETL and EHL are set to 1. TLFS: Temperature Logging Format Selection b2 This bit specifies the format used to store temperature readings in the data log memory. If this bit is 0, the data will be stored in 8-bit format. If this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit format, the most-significant byte is stored at the lower address.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 20 of 52 Bit Description Bit(s) Definition HLFS: Humidity Logging Format Selection b3 This bit specifies the format used to store humidity readings in the data log memory. If this bit is 0, the data will be 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. RO: Rollover Control b4 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 beginning, overwriting previously collected data. If this bit is 0, the logging and conversions will stop once the data log memory is full. However, the RTC will continue to run and the MIP bit will remain set until the Stop Mission command is performed. SUTA: Start Mission upon Temperature Alarm b5 This bit specifies whether a mission begins immediately (includes delayed start) or if a temperature alarm will be required to start the mission. If this bit is 1, the device will perform a temperature conversion at the selected sample rate and begin with data logging only if an alarming temperature (high alarm or low alarm) was found. The first logged temperature will be when the alarm occurred. However, the Mission Sample Counter will not increment. The Start Upon Tempera- ture Alarm function is only available if temperature logging is enabled (ETL = 1). 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 i Buttons 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0214h BOR 1 1 1 HHF HLF THF TLF 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 Bit Description Bit(s) Definition TLF: Temperature Low Alarm Flag b0 If this bit reads 1, there was at least one temperature conversion during a mission revealing a temperature equal to or lower than the value in the Temperature Low Alarm Register. A forced conversion can affect the TLF bit. This bit can also be set with the initial alarm in the SUTA = 1 mode. THF: Temperature High Alarm Flag b1 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. HLF: Humidity Low Alarm Flag b2 If this bit reads 1, there was at least one humidity reading during a mission revealing a value equal to or lower than the value in the Humi- dity Low Alarm Register. A forced conversion can affect the HLF bit. HHF: Humidity High Alarm Flag b3 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 Humi- dity High Alarm Register. A forced conversion can affect the HHF bit. BOR: Battery On Reset Alarm b7 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.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 21 of 52 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0215h 1 1 0 WFTA MEMCLR 0 MIP 0 There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function. Register Details Bit Description Bit(s) Definition MIP: Mission In Progress b1 If this bit reads 1 the device has been set up for a mission and this mission is still in progress. The MIP bit returns from logic 1 to logic 0 when a mission is ended. See function commands Start Mission and Stop Mission. MEMCLR: Memory Cleared b3 If this bit reads 1, the Mission Time Stamp, Mission Sample Counter, as well as 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 sections. The MEMCLR bit returns to 0 as soon as a new mission is started by using the Start Mission command. The memory has to be cleared in order for a mission to start. WFTA: Waiting for Temperature Alarm b4 If this bit reads 1, the Mission Start upon Temperature Alarm was selected and the Start Mission command was successfully executed, but the device has not yet experienced 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. 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0216h Delay Low Byte 0217h Delay Center Byte 0218h Delay High Byte 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 22 of 52 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0219h 0 10 Seconds Single Seconds 021Ah 0 10 Minutes Single Minutes 021Bh 0 12/24 20h. AM/PM 10h. Single Hours 021Ch 0 0 10 Date Single Date 021Dh CENT 0 0 10m. Single Months 021Eh 10 Years Single Years 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0220h Low Byte 0221h Center Byte 0222h High Byte 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 i Button. Device Sample Counter Register Map ADDR b7 b6 b5 b4 b3 b2 b1 b0 0223h Low Byte 0224h Center Byte 0225h High Byte There is only read access to this register. The Device Sample Counter is reset to zero when the i Button 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. The Device Configuration Byte is used to allow the master to distinguish between the DS2422 chip, and the DS1923, DS1922L, and DS1922T i Buttons. The table below shows the codes assigned to the various devices.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 23 of 52 Device Configuration Byte ADDR b7 b6 b5 b4 b3 b2 b1 b0 0226h 0 0 0 0 0 0 0 0 DS2422 0226h 0 0 1 0 0 0 0 0 DS1923 0226h 0 1 0 0 0 0 0 0 DS1922L 0226h 0 1 1 0 0 0 0 0 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0227h EPW 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0228h RP7 RP6 RP5 RP4 RP3 RP2 RP1 RP0 0229h RP15 RP14 RP13 RP12 RP11 RP10 RP9 RP8 /g190 /g190 /g190 022Eh RP55 RP54 RP53 RP52 RP51 RP50 RP49 RP48 022Fh RP63 RP62 RP61 RP60 RP59 RP58 RP57 RP56 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 ADDR b7 b6 b5 b4 b3 b2 b1 b0 0230h FP7 FP6 FP5 FP4 FP3 FP2 FP1 FP0 0231h FP15 FP14 FP13 FP12 FP11 FP10 FP9 FP8 /g190 /g190 /g190 0236h FP55 FP54 FP53 FP52 FP51 FP50 FP49 FP48 0237h FP63 FP62 FP61 FP60 FP59 FP58 FP57 FP56 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.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 24 of 52 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 8192 8-bit entries Temperature or Humidity data 4096 16-bit entries Temperature or Humidity data 1000h 2FFFh 1000h 2FFFh ETL = 1; EHL = 0 or ETL = 0; EHL = 1 TLFS = HLFS = 0 ETL = 1; EHL = 0 or ETL = 0; EHL = 1 TLFS = HLFS = 1 With 16-bit format, the most-significant byte is stored at the lower address.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 26 of 52 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 a nd 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 address is called byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad stores incoming data beginning at the byte offset 1Ch and is full after only 4 bytes. The corresponding ending offset

and executed. Writing data to the scratchpad clears this flag. Figure 8. ADDRESS REGISTERS the data to the requested location beginning at the target address. commands described below. See Memory Access Conflicts for details and remedies. incomplete, its content is ignored and the partial byte flag PF is set. a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by the master.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 28 of 52 This CRC is generated using the CRC16 polynomial by fi rst clearing the CRC generator and then shifting in the command code (0Fh) of the Write Scratchpad command, the Target Addresses TA1 and TA2 as supplied by the master and all the data bytes. If the ending offset is 11111b, the master may send 16 read time slots and will receive the inverted CRC16 generated by the DS1923. Note that both register pages are write-protected during a mission. Although the Write Scratchpad command will work normally at any time, the subsequent copy scratchpad to a register page will fail during a mission. Read Scratchpad Command [AAh] This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad command, the master begins reading. The first 2 bytes will be the target address. The next byte will be the ending offset/data status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0), as shown in Figure 8. The master may continue reading data until the end of the scratchpad after which it will receive an inverted CRC16 of the command code, Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target address. After the CRC is read, the bus master will read logical 1s from the DS1923 until a reset pulse is issued. Copy Scratchpad with Password [99h] This command is used to copy data from the scratchpad to the writable memory sections. After issuing the Copy Scratchpad command, the master must provide a 3-byte authorization pattern, which can be obtained by reading the scratchpad for verification. This pattern must exactly match the data contained in the three address registers (TA1, TA2, E/S, in that order). Next the master must transmit the 64-bit full-access password. If passwords are enabled and the transmitted password is different from the stored full-access password, the Copy Scratchpad with Password command will fail. Then the device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device tests the 3-byte authorization code. If the authorization code pattern matches, the AA (Authorization Accepted) flag is set and the copy begins. A pattern of alternating 1s and 0s are transmitted after the data has been copied until the master issues a reset pulse. While the copy is in progress any attempt to reset the part is ignored. Copy typically takes 2µs per byte. The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset through the ending offset will be copied, starting at the target address. The AA flag remains at logic 1 until it is cleared by the next Write Scratchpad command. With suitable password, the copy scratchpad always functions for the 16 pages of data memory and the 2 pages of calibration memory. While a mission is in progress, write attempts to the register pages will not be successful. The AA bit (Authorization Accepted) remaining at 0 will indicate this. Read Memory with Password and CRC [69h] The Read Memory with CRC command is the general function to read from the device. This command generates and transmits a 16-bit CRC following the last data byte of a memory page. After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte address that indicates a starting byte location. Next the master must transmit one of the 64-bit passwords. If passwords are enabled and the transmitted password does not match one of the stored passwords, the Read Memory with Password and CRC command fails. The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the master reads data from the DS1923 beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus master sends 16 additional read data time slots and rece ive the inverted 16-bit CRC. With subsequent read-data time slots the master will receive data starting at the beginning of the next memory page followed again by the CRC for that page. This sequence continues until the bus master resets the device. When trying to read the passwords or memory areas that are marked as "reserved", the DS1923 transmits 00h or FFh bytes, respectively. The CRC at the end of a 32-byte memory page is based on the data as it was transmitted. With the initial pass through the Read Memory with CRC flow, the 16-bit CRC value is the result of shifting the command byte into the cleared CRC generator followed by the 2 address bytes and the contents of the data memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of the last page is read, the bus master receives logical 1s from the DS1923 until a reset pulse is issued. The Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 29 of 52 Figure 9-1. MEMORY/CONTROL FUNCTION FLOW CHART Master TX Memory or Control Fkt. Command 0FH Write Scratchpad Master TX TA1 (T7:T0) Master TX TA2 (T15:T8) DS1923 sets Scratch- pad Offset = (T4:T0) and Clears (PF, AA) Master TX Data Byte to Scratchpad Offset DS1923 sets (E4:E0) = Scratchpad Offset Master TX Reset? Scratch- pad Offset = 11111b? Master RX CRC16 of Command, Address Data DS1923 Incre- ments Scratch- pad Offset Master RX "1"s Master TX Reset? Master TX Reset? Partial Byte Written? PF = 1 AAH Read Scratchpad Master RX TA1 (T7:T0) Master RX TA2 (T15:T8) Master RX Ending Offset with Data Status (E/S) Master TX Reset? Scratch- pad Offset = 11111b? Master RX CRC16 of Command, Address Data, E/S Byte, and Data Starting at the Target Address DS1923 Incre- ments Scratch- pad Offset Master RX "1"s Master TX Reset? DS1923 sets Scratch- pad Offset = (T4:T0) Master RX Data Byte from Scratchpad Offset From ROM Functions Flow Chart (Figure 11) To ROM Functions Flow Chart (Figure 11) N Y N Y N Y N Y N Y N Y N Y N Y N Y N Y

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 30 of 52 Figure 9-2. MEMORY/CONTROL FUNCTION FLOW CHART 99H Copy Scrpd. [w/PW] Master TX E/S Byte Authorization Code Match? DS1923 Copies Scratchpad Data to Memory Copying Finished Master TX Reset? AA = 1 Master TX TA1 (T7:T0), TA2 (T15:T8) Master TX 64-Bits [Password] Password Accepted? Master RX "1"s DS1923 TX "0" DS1923 TX "1" Master TX Reset? N Y N Y N Y N Y Master TX Reset? Master RX "1"s N Y N Y N Y Authorization Code

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 31 of 52 Figure 9-3. MEMORY/CONTROL FUNCTION FLOW CHART 69H Read Mem. [w/PW]&CRC Master TX 64-Bits [Password] Master TX Reset? CRC OK? Master RX "1"s DS1923 sets Memory Address = (T15:T0) Master RX Data Byte from Memory Address Master TX TA1 (T7:T0), TA2 (T15:T8) Password Accepted? DS1923 Incre- ments Address Counter End of Page? Master RX CRC16 of Command, Address, Data st Pass); CRC16 of Data (Subsequent Passes) End of Memory? Master TX Reset? Master TX Reset N Y N Y N Y N Y N Y N Y N Y Decision made by DS1923 Decision made by Master

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 32 of 52 Figure 9-4. MEMORY/CONTROL FUNCTION FLOW CHART 96H Clear Mem. [w/PW] 55H Forced Conversion? Master TX 64-Bits [Password] N Y N Y Mission in Progress? DS1923 clears Mission Time Stamp, Mission Samples Counter, Alarm Flags DS1923 sets MEMCLR = 1 Password Accepted? Master TX Reset? N Y N Y N Y Mission in Progress? DS1923 Performs a Temp. Conversion DS1923 copies Result to Address 020C/Dh DS1923 Performs a Humidity Conversion DS1923 copies Result to Address 020E/Fh N Y Master TX Reset? N Y Master TX FFh dummy byte Master TX FFh dummy byte

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 33 of 52 Figure 9-5. MEMORY/CONTROL FUNCTION FLOW CHART CCH Start Mission [w/PW] Master TX 64-Bits [Password] Master TX Reset? DS1923 Initiates Mission Start Delay Process N Y Mission in Progress? DS1923 sets MIP = 1 MEMCLR = 0 Password Accepted? MEMCLR = 1? N Y N Y N Y N Y Master TX FFh dummy byte 33H Stop Mission [w/PW] Master TX 64-Bits [Password] N Y Mission in Progress? DS1923 sets MIP = 0 WFTA = 0 Password Accepted? Master TX Reset? N Y N Y N Y Master TX FFh dummy byte N DS1923 Waits for 1 Minute Mission Start Delay Process DS1923 Sets WFTA=1 Start Delay Counter = 0? Y DS1923 decrements Start Delay Counter DS1923 sets WFTA=0 and logs first sample N Y Temp. Alarm? DS1923 Performs 8-bit Temp. Conversion N MIP = 0? Y DS1923 Waits One Sample Period SUTA = 1? Y N DS1923 copies RTC Data to Mission Time Stamp Register DS1923 Starts Logging Taking 1st Sample End Of Process DS1923 Waits One Sample Period If SUTA = 1, this is the 2 nd sample. The Mission Sample Counter will not increment.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 34 of 52 Clear Memory with Password [96h] The Clear Memory with Password command is used to prepare the device for another mission. This command is only executed if no mission is in progress. After the command code the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is in progress, the Clear Memory with Password command will fail. The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the device will clear the Mission Time Stamp, Mission Sample Counter, and all alarm flags of the Alarm Status Register. After these cells are cleared, the MEMCLR bit of the General Status Register reads 1 to indicate the successful execution of the Clear Memory with Password command. Clearing of the data log memory is not necessary because the Mission Sample Counter indicates how many entries in the data log memory are valid. Forced Conversion [55h] The Forced Conversion command can be used to measure the temperature and humidity without starting a mission. After the command code the master has to send one FFh byte to get the conversion started. The conversion result is found as 16-bit value in the Latest Temperature Conversion Result and Latest Humidity Conversion Result registers. This command is only executed if no mission is in progress (MIP = 0). It cannot be interrupted and takes maximum 666ms to complete. During this time memory access through the 1-Wire interface is blocked. The device behaves the same way as during a mission when the sampling interferes with a memory/control function command. See Memory Access Conflicts for details. A forced conversion must not be attempted while the RTC oscillator is stopped. This causes the device to enter into an unrecoverable state. Start Mission with Password [CCh] The DS1923 uses a control function command to start a mission. A new mission can only be started if the previous mission has been ended and the memory has been cleared. After the command code, the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is in progress, the Start Mission with Password command will fail. The device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device starts a mission. If SUTA = 0, the sampling begins as soon as the mission start delay is over. If SUTA = 1, the first sample is written to the data log memory at the time the temperature alarm occurred. However, the Mission Sample Counter does not increment. One sample period later, the Mission Time Stamp will be set and the regular sampling and logging begins. While the device is waiting for a temperature alarm to occur, the WFTA flag in the general status register will read 1. During a mission there is only read access to the Register Pages. Stop Mission with Password [33h] The DS1923 uses a control function command to stop a mission. Only a mission that is in progress can be stopped. After the command code, the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are enabled and the transmitted password is different from the stored full-access password or a mission is not in progress, the Stop Mission with Password command will fail. The device stops communicating and waits for a reset pulse. If the password was correct or if passwords were not enabled, the device clears the MIP bit in the General Status Register and restore write access to the Register Pages. The WFTA bit is not cleared. See the description of the General Status Register for a method to clear the WFTA bit. MEMORY ACCESS CONFLICTS While a mission is in progress or while the device is waiting for a temperature alarm to start a mission, periodically a temperature and/or humidity sample is taken and logged. This "internal activity" has priority over 1-Wire communication. As a consequence, device-specific commands (excluding ROM function commands and 1-Wire reset) will not perform properly when internal and "external" activities interfere with each other. Not affected are the commands Start Mission, Forced Conversion, and Clear Memory because they are not applicable while a mission is in progress or while the device is waiting for a temperature alarm. The table below explains how the remaining five commands are affected by internal activity, how to detect this interference and how to work around it.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 35 of 52 Command Indication of Interference Remedy Write Scratchpad The CRC16 at the end of the command flow reads FFFFh. Wait 0.5 seconds, 1-Wire reset, address the device, repeat Write Scratchpad with the same data, and check the validity of the CRC16 at the end of the command flow. Alternatively, use Read Scratchpad to verify data integrity. Read Scratchpad The data read changes to FFh bytes or all bytes received are FFh, including the CRC at the end of the command flow. Wait 0.5 seconds, 1-Wire reset, address the device, repeat Read Scratchpad, and check the validity of the CRC16 at the end of the command flow. Copy Scratchpad The device behaves as if authorization code or password was not valid or as if the copy function would not end. Wait 0.5 seconds, 1-Wire reset, address the device, issue Read Scratchpad and check the AA-bit of the E/S byte. If the AA-bit is set, Copy Scratchpad was successful. Read Memory with CRC The data read changes to all FFh bytes or all bytes received are FFh, including the CRC at the end of the command flow, despite a valid password. Wait 0.5 seconds, 1-Wire reset, address the device, repeat Read Memory with CRC, and check the validity of the CRC16 at the end of the memory page. Stop Mission The general Status register at address 215h reads FFh or the MIP bit is 1 while bits 0, 2, and 5 are 0. Wait 0.5 seconds, 1-Wire reset, address the device, and repeat Stop Mission. Perform a 1-Wire reset, address the device, read the general Status register at address 215h and check the MIP-bit. If the MIP-bit is 0, Stop Mission was successful. The interference is more likely to be seen with a high sample rate (1 sample every second) and with high-resolution logging, which can last up to 666ms when both temperature and humidity are recorded. With lower sample rates interference may hardly be visible at all. In any case, when writing driver software, it is important to know about the possibility of interference and to take measures to work around it. 1-WIRE BUS SYSTEM The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1923 is a slave device. The bus master is typically a microcontroller. The discussion of this bus system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling (signal types and timing). The 1-Wire protocol defines bus transactions in terms of the bus state during specific time slots that are initiated on the falling edge of sync pulses from the bus master. For a more detailed protocol description, refer to Chapter 4 of the Book of DS19xx i Button Standards. HARDWARE CONFIGURATION The 1-Wire bus has only a single line by definition; it is important that each device on the bus be able to drive it at the appropriate time. To facilitate this, each device attached to the 1-Wire bus must have open drain or tri-state outputs. The 1-Wire port of the DS1923 is open-drain with an internal circuit equivalent to that shown in Figure 10. A multidrop bus consists of a 1-Wire bus with multiple slaves attached. At standard speed the 1-Wire bus has a maximum data rate of 16.3kbps. The speed can be boosted to 142kbps by activating the Overdrive mode. The DS1923 is not guaranteed to be fully compliant to the i Button Standard. Its maximum data rate in standard speed mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the network size and load conditions. The DS1923 requires a pullup resistor of maximum 2.2k /g87 at any speed. The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be left in the idle state if the transaction is to resume. If this does not occur and the bus is left low for more than 16µs (Overdrive speed) or more than 120µs (standard speed), one or more devices on the bus may be reset. Note that the DS19233 does not quite meet the full 16µs maximum low time of the normal 1-Wire bus Overdrive timing. With the DS1923 the bus must be left low for no longer than 12µs at Overdrive to ensure that no DS1923 on the 1-Wire bus performs a reset. The DS1923 communicates properly when used in conjunction with a DS2480B or DS2490 1-Wire driver and adapters that are based on these driver chips.

Figure 10. HARDWARE CONFIGURATION result). The resultant family code and 48-bit serial number results in a mismatch of the CRC. single or multiple devices on the bus.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 37 of 52 devices exist with both states of the bit. By choosing which state to write, the bus master branches in the romcode tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify the registration numbers of the remaining devices. Refer to App Note 187: 1-Wire Search Algorithm for a detailed discussion, including an example. Conditional Search [ECh] The Conditional Search ROM command operates similarly to the Search ROM command except that only those devices, which fulfill certain conditions, participate in the search. This function provides an efficient means for the bus master to identify devices on a multidrop system that have to signal an important event. After each pass of the conditional search that successfully determined the 64-bit ROM code for a specific device on the multidrop bus, that particular device can be individually accessed as if a Match ROM had been issued, since all other devices have dropped out of the search process and will be waiting for a reset pulse. The DS1923 responds to the conditional search if one of the five alarm flags of the Alarm Status Register (address 0214h) reads 1. The humidity and temperature alarm only occurs if enabled (see Temperature Sensor Alarm and Humidity Alarm). The BOR alarm is always enabled. The first alarm that occurs makes the device respond to the Conditional Search command. Skip ROM [CCh] This command can save time in a single-drop bus system by allowing the bus master to access the memory functions without providing the 64-bit ROM code. If more than one slave is present on the bus and, for example, a Read command is issued following the Skip ROM command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns produce a wired-AND result). Resume Command [A5h] The DS1923 needs to be accessed several times before a mission starts. In a multidrop environment this means that the 64-bit ROM code after a Match ROM command has to be repeated for every access. To maximize the data throughput in a multidrop environment, the Resume function was implemented. This function checks the status of the RC bit and, if it is set, directly transfers control to the Memory/Control functions, similar to a Skip ROM command. The only way to set the RC bit is through successfully executing the Match ROM, Search ROM or Overdrive Match ROM command. Once the RC bit is set, the device can repeatedly be accessed through the Resume Command function. Accessing another device on the bus will clear the RC bit, preventing two or more devices from simultaneously responding to the Resume Command function. Overdrive Skip ROM [3Ch] On a single-drop bus this command can save time by allowing the bus master to access the memory/control func- tions without providing the 64-bit ROM code. Unlike the normal Skip ROM command, the Overdrive Skip ROM sets the DS1923 in the Overdrive mode (OD = 1). All communication following this command has to occur at Overdrive speed until a reset pulse of minimum 690µs duration resets all devices on the bus to standard speed (OD = 0). When issued on a multidrop bus this command will set all Overdrive-supporting devices into Overdrive mode. To subsequently address a specific Overdrive-supporting device, a reset pulse at Overdrive speed has to be issued followed by a Match ROM or Search ROM command sequence. This speeds up the time for the search process. If more than one slave supporting Overdrive is present on the bus and the Overdrive Skip ROM command is followed by a Read command, data collision occurs on the bus as multiple slaves transmit simultaneously (open-drain pulldowns will produce a wired-AND result). Overdrive Match ROM [69h] The Overdrive Match ROM command followed by a 64-bit ROM sequence transmitted at Overdrive Speed allows the bus master to address a specific DS1923 on a multidrop bus and to simultaneously set it in Overdrive mode. Only the DS1923 that exactly matches the 64-bit ROM sequence will respond to the subsequent memory/control function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive Match command remains in Overdrive mode. All overdrive-capable slaves return to standard speed at the next Reset Pulse of minimum 690µs duration. The Overdrive Match ROM command can be used with a single or multiple devices on the bus.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 38 of 52 Figure 11-1. ROM FUNCTIONS FLOW CHART From Figure 11 nd PartTo Memory Functions Flow Chart (Figure 9) Master TX Bit 0 Master TX Bit 63 Master TX Bit 1 RC = 1 DS1923 TX CRC Byte DS1923 TX Serial Number (6 Bytes) DS1923 TX Family Code (1 Byte) Bit 0 Match? Y N Bit 1 Match? Y N Bit 63 Match? Y N DS1923 TX Bit 0 DS1923 TX Bit 0 Master TX Bit 0 DS1923 TX Bit 1 DS1923 TX Bit 1 Master TX Bit 1 DS1923 TX Bit 63 DS1923 TX Bit 63 Master TX Bit 63 RC = 1 Bit 0 Match? Y N Bit 1 Match? Y N Bit 63 Match? Y N To Figure 11 nd Part RC = 0RC = 0 RC = 0RC = 0 YY YY NF0h Search ROM Command? N55h Match ROM Command? N ECh Cond. Search Command? N33h Read ROM Command? To Figure 11 nd Part From Memory Functions Flow Chart (Figure 9) Bus Master TX ROM Function Command DS1923 TX Presence Pulse OD Reset Pulse? N Y OD = 0 Bus Master TX Reset Pulse From Figure 11, 2 nd Part Condition Met? Y N DS1923 TX Bit 0 DS1923 TX Bit 0 Master TX Bit 0 DS1923 TX Bit 1 DS1923 TX Bit 1 Master TX Bit 1 DS1923 TX Bit 63 DS1923 TX Bit 63 Master TX Bit 63 RC = 1 Bit 0 Match? Y N Bit 1 Match? Y N Bit 63 Match? Y N

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 39 of 52 Figure 11-2. ROM FUNCTIONS FLOW CHART From Figure 11 1st Part From Figure 11 1st Part To Figure 11, 1st Part RC = 1 ? N Y RC = 0 ; OD = 1 Master TX Bit 0 Master TX Bit 63 Master TX Bit 1 RC = 1 Bit 0 Match? Y N Bit 1 Match? Y N Bit 63 Match? Y N Y N69h Overdrive Match ROM? RC = 0 ; OD = 1 Master TX Reset ? Y N Master TX Reset ? N Y Y N3Ch Overdrive Skip ROM? Y NA5h Resume Command? RC = 0 Y NCCh Skip ROM Command? To Figure 11 1st Part

communicates at standard speed. While in Overdrive Mode the fast timing applies to all waveforms. logical level, not triggering any events. Figure 12. INITIALIZATION PROCEDURE “RESET AND PRESENCE PULSES” pulse, the master must test the logical state of the 1-Wire line at tMSP. 480µs at standard speed and 48µs at Overdrive speed to accommodate other 1-Wire devices. write and read time slots are illustrated in Figure 13. a write time slot and how long data will be valid during a read-time slot.

tREC before it is ready for the next time slot. Figure 13. READ/WRITE TIMING DIAGRAM

recovery time tREC for the DS1923 to get ready for the next time slot. reduces the magnitude of noise injected by the slave device itself. The 1-Wire front end of the DS1923 differs from traditional slave devices in four characteristics. which has different values for standard and Overdrive speed. 2) There is additional low-pass filtering in the circuit that detects the falling edge at the beginning of a time slot. This reduces the sensitivity to high-frequency noise. This additional filtering does not apply at Overdrive speed. below VTH - VHY, it will not be recognized (Figure 14, Case A). The hysteresis is effective at any 1-Wire speed. taken as beginning of a new time slot (Figure 14, Case C, tGL /g179 tREH). Figure 14. NOISE SUPPRESSION SCHEME

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 44 of 52 Command-Specific 1-Wire Communication Protocol—Legend Symbol Description RST 1-Wire Reset Pulse generated by master PD 1-Wire Presence Pulse generated by slave Select Command and data to satisfy the ROM function protocol WS Command "Write Scratchpad" RS Command "Read Scratchpad" CPS Command "Copy Scratchpad with Password" RMC Command "Read Memory with Password & CRC" CM Command "Clear Memory with Password " FC Command "Forced Conversion" SM Command "Start Mission with Password" STP Command "Stop Mission with Password" TA Target Address TA1, TA2 TA-E/S Target Address TA1, TA2 with E/S byte <data to EOS> Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh <data to EOP> Transfer of as many data bytes as are needed to reach the end of a memory page <data to EOM> Transfer of as many data bytes as are needed to reach the end of the data log memory <PW/dummy> Transfer of 8 bytes that either represent a valid password or acceptable dummy data <32 bytes> Transfer of 32 bytes <data> Transfer of an undetermined amount of data FFh Transmission of one byte FFh CRC16\\ Transfer of an inverted CRC16 FF loop Indefinite loop where the master reads FF bytes AA loop Indefinite loop where the master reads AA bytes Command-Specific 1-Wire Communication Protocol—Color Codes Master to slave Slave to master Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail) RST PD Select WS TA <data to EOS> CRC16\\ FF loop Read Scratchpad (Cannot Fail) RST PD Select RS TA-E/S <data to EOS> CRC16\\ FF loop Copy Scratchpad with Password (Success) RST PD Select CPS TA-E/S <PW/dummy> AA loop

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 45 of 52 Copy Scratchpad with Password (Fail TA-E/S or Password) RST PD Select CPS TA-E/S <PW/dummy> FF loop Read Memory with Password and CRC (Success) RST PD Select RMC TA <PW/dummy> <data to EOP> CRC16\\ <32 bytes> CRC16\\ FF loop Read Memory with Password and CRC (Fail Password or Address) RST PD Select RMC TA <PW/dummy> FF loop Clear Memory with Password RST PD Select CM <PW/dummy> FFh FF loop To verify success, read the General Status Register at address 0215h. If MEMCLR is 1, the command was executed successfully. Forced Conversion RST PD Select FC FFh FF loop To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Sample Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully. Start Mission with Password RST PD Select SM <PW/dummy> FFh FF loop To verify success, read the General Status Register at address 0215h. If MIP is 1 and MEMCLR is 0, the command was executed successfully. Stop Mission with Password RST PD Select STP <PW/dummy> FFh FF loop To verify success, read the General Status Register at address 0215h. If MIP is 0, the command was executed successfully. Loop

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 46 of 52 MISSION EXAMPLE: PREPARE AND START A NEW MISSION Assumption: The previous mission has been ended by using the Stop Mission command. Passwords are not enabled. The device is a DS1923. Starting a mission requires three steps: Step 1: clear the data of the previous mission Step 2: write the setup data to register page 1 Step 3: start the mission STEP 1 Clear the previous mission. With only a single device connected to the bus master, the communication of step 1 looks like this: MASTER MODE DATA (LSB FIRST) COMMENTS TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue “skip ROM” command TX 96h Issue “clear memory” command TX <8 FFh bytes> Send dummy password TX FFh Send dummy byte TX (Reset) Reset pulse RX (Presence) Presence pulse STEP 2 During the setup, the device needs to learn the following information: /g167/g32Time and Date /g167/g32Sample Rate /g167/g32Alarm Thresholds /g167/g32Alarm Controls (Response to Conditional Search) /g167/g32General Mission Parameters (e.g., Channels to Log and Logging Format, Rollover, Start Mode) /g167/g32Mission Start Delay The following data will setup the DS1923 for a mission that logs temperature and humidity using 8-bit format for both. Such a mission could last up to 28 days until the 8192-byte data log memory is full. ADDRESS DATA EXAMPLE VALUES FUNCTION 0200h 00h 0201h 30h 15:30:00 hours Time 0202h 15h 0203h 15h 0204h 05h 15 th of May in 2004 Date 0205h 04h 0206h 0Ah Every 10 minutes (EHSS = 0) Sample rate 0207h 00h 0208h 66h 10°C low Temperature alarm 0209h 7Ah 20°C high Threshold 020Ah 6Fh 40%RH low Humidity alarm threshold, 020Bh 9Eh 70%RH high No software correction used 020Ch FFh 020Dh FFh (don’t care) Clock through 020Eh FFh Read-only registers 020Fh FFh

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 47 of 52 ADDRESS DATA EXAMPLE VALUES FUNCTION 0210h 03h Enable high and low alarm Temperature Alarm Control 0211h FFh Enable high and low alarm Humidity Alarm Control 0212h 01h On (enabled), EHSS = 0 (low sample rate) RTC oscillator control, sample rate selection 0213h C3h Normal start; no rollover; 8-bit logging General mission control 0214h FFh (don’t care) Clock through 0215h FFh Read-only registers 0216h 5Ah 0217h 00h 90 minutes Mission start delay 0218h 00h With only a single device connected to the bus master, the communication of step 2 looks like this: MASTER MODE DATA (LSB FIRST) COMMENTS TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue “skip ROM” command TX 0Fh Issue “write scratchpad” command TX 00h TA1, beginning offset=00h TX 02h TA2, address=02 00h TX <25 data bytes> Write 25 bytes of data to scratchpad TX <7 FFh bytes> Write through the end of the scratchpad TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue “skip ROM” command TX AAh Issue “read scratchpad” command RX 00h Read TA1, beginning offset=00h RX 02h Read TA2, address=02 00h RX 1Fh Read E/S, ending offset=1Fh, flags=0h RX <32 data bytes> Read scratchpad data and verify TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue “skip ROM” command TX 99h Issue “copy scratchpad” command TX 00h TX 02h TX 1Fh TA1 TA2 (AUTHORIZATION CODE) E/S TX <8 FFh bytes> Send dummy password TX (Reset) Reset pulse RX (Presence) Presence pulse

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 48 of 52 STEP 3 Start the new mission. With only a single device connected to the bus master, the communication of step 3 looks like this: MASTER MODE DATA (LSB FIRST) COMMENTS TX (Reset) Reset pulse RX (Presence) Presence pulse TX CCh Issue “skip ROM” command TX CCh Issue “start mission” command TX <8 FFh bytes> Send dummy password TX FFh Send dummy byte TX (Reset) Reset pulse RX (Presence) Presence pulse If step 3 was successful, the MIP bit in the General Status Register will be 1, the MEMCLR bit will be 0 and the mission start delay will count down. SOFTWARE CORRECTION ALGORITHM FOR TEMPERATURE The accuracy of high-resolution temperature conversion results (forced conversion as well as temperature logs) can be improved through a correction algorithm. The data needed for this software correction is stored in the calibration memory (memory page 18). It consists of reference temperature (Tr) and conversion result (Tc) for two different temperatures, as shown below. See section Temperature Conversion for the binary number format. ADDRESS DESIGNATOR DESCRIPTION 0240h Tr2H Cold reference temperature, high-byte 0241h Tr2L Cold reference temperature, low-byte 0242h Tc2H Conversion result at cold reference temperature, high-byte 0243h Tc2L Conversion result at cold reference temperature, low-byte 0244h Tr3H Hot reference temperature, high-byte 0245h Tr3L Hot reference temperature, low-byte 0246h Tc3H Conversion result at hot reference temperature, high-byte 0247h Tc3L Conversion result at hot reference temperature, low-byte The software correction algorithm requires two additional values, which are not stored in the device. For the DS1923 these values are Tr1 = 60°C and Offset = 41. The correction algorithm consists of two steps, preparation and execution. The preparation step first converts temperature data from binary to decimal °C format. Next three coefficients A, B, and C are computed. In the execution step the temperature reading as delivered by the DS1923 is first converted from the low/high-byte format (TcL, TcH) to °C (Tc) and then corrected to Tcorr. Once step 1 is performed, the three coefficients can be used repeatedly to correct any temperature reading and temperature log of the same device. Step 1. Preparation Tr1 = 60 Offset = 41 Tr2 = Tr2H/2 + Tr2L/512 - Offset (convert from binary to °C) Tr3 = Tr3H/2 + Tr3L/512 - Offset (convert from binary to °C) Tc2 = Tc2H/2 + Tc2L/512 - Offset (convert from binary to °C) Tc3 = Tc3H/2 + Tc3L/512 - Offset (convert from binary to °C) Err2 = Tc2 - Tr2 Err3 = Tc3 - Tr3 Err1 = Err2 B = (Tr2 2 - Tr12) * (Err3 - Err1)/[(Tr22 - Tr12) * (Tr3 - Tr1) + (Tr32 - Tr12) * (Tr1 - Tr2)] A = B * (Tr1 – Tr2) / (Tr22 - Tr12) C = Err1 - A * Tr12 - B * Tr1

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 49 of 52 Step 2. Execution Tc = TcH/2 + TcL/512 - Offset (convert from binary to °C) Tcorr = Tc - (A * Tc2 + B * Tc + C) (the actual correction) Numerical Correction Example Converted Data from Calibration Memory Error Values Tr2 = -10.1297°C Tr3 = 24.6483°C Tc2 = -10.0625°C Tc3 = 24.5°C Err2 = 0.0672°C Err3 = -0.1483°C Err1 = Err2 Resulting Correction Coefficients Application of Correction Coefficients to Sample Reading B = -0.008741 A = 0.000175/°C C = -0.039332°C Tc = 22.500000°C Tcorr = 22.647275°C NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are found on various websites and are included in cross-compilers. SOFTWARE CORRECTION ALGORITHM FOR HUMIDITY The accuracy of humidity conversion results (forced conversion as well as logged data) can be improved through a correction algorithm. The data needed for this software correction is stored in the calibration memory (memory page 18). It consists of reference humidity (Hr) and conversion result (Hc) for three different humidity levels, as shown below. The data is taken at 25°C. Address Designator Description 0248h Hr1H Low reference humidity, high-byte 0249h Hr1L Low reference humidity, low-byte 024Ah Hc1H Conversion result at low reference humidity, high-byte 024Bh Hc1L Conversion result at low reference humidity, low-byte 024Ch Hr2H Medium reference humidity, high-byte 024Dh Hr2L Medium reference humidity, low-byte 024Eh Hc2H Conversion result at medium reference humidity, high-byte 024Fh Hc2L Conversion result at medium reference humidity, low-byte 0250h Hr3H High reference humidity, high-byte 0251h Hr3L High reference humidity, low-byte 0252h Hc3H Conversion result at high reference humidity, high-byte 0253h Hc3L Conversion result at high reference humidity, low-byte The correction algorithm consists of two steps: preparation and execution. The preparation step first converts humidity data from binary to decimal %RH format. Next three coefficients A, B, and C are computed. In the execution step the humidity reading as delivered by the DS1923 (raw data) is first converted from the low/high-byte format (HcL, HcH) to %RH (Hc) and then corrected to Hcorr. Once step 1 is performed, the three coefficients can be used repeatedly to correct any humidity reading and humidity log of the same device.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 50 of 52 Step 1. Preparation For the humidity data in the calibration memory, the lower four bits of each low byte are set to 0. This simplifies the conversion from the binary data format to raw %RH values to a one-line equation. Hr1 = ((Hr1H * 256 + Hr1L) * 5.02/65536 - 0.958)/0.0307 (convert from binary to %RH) Err1 = Hc1 - Hr1 Err2 = Hc2 - Hr2 Err3 = Hc3 - Hr3 B = [(Hr2 2 - Hr12) * (Err3 - Err1) + Hr3²*(Err1 - Err2) + Hr1² * (Err2 - Err1)]/[(Hr22 - Hr12) * (Hr3 - Hr1) + (Hr32 - Hr12) * (Hr1 - Hr2)] A = [Err2 - Err1 + B * (Hr1 - Hr2)] / (Hr2 2 - Hr12) C = Err1 - A * Hr1 2 - B * Hr1 Step 2. Execution Hc = ((HcH * 256 + HcL) * 5.02/65536 - 0.958)/0.0307 (convert from binary to %RH) Hcorr = Hc - (A * Hc2 + B * Hc + C) (the actual correction) Numerical Correction Example Converted Data from Calibration Memory Error Values Hr1 = 20%RH Hr2 = 60%RH Hr3 = 90%RH Hc1 = 17.65%RH Hc2 = 56.41%RH Hc3 = 89.57%RH Err1 = -2.35%RH Err2 = -3.59%RH Err3 = -0.43%RH Resulting Correction Coefficients Application of Correction Coefficients to Sample Reading B = -0.186810 A = 0.001948/%RH C = 0.607143%RH Hc = 8.9%RH Hcorr = 9.8%RH NOTE: The software correction requires floating point arithmetic (24-bit or better). Suitable math libraries for microcontrollers are found on various websites and are included in cross-compilers.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 51 of 52 RH TEMPERATURE COMPENSATION The data for the software correction of humidity is taken at 25°C. Since the temperature characteristics of the humidity sensor are known, humidity readings taken at other temperatures can be corrected, provided the temperature at the time of the humidity conversion is also known. Therefore, to obtain the most accurate humidity results, both temperature and humidity should be logged. Temperature compensation uses the following equation: HTcorr = (Hcorr * K + /g97*(T-25°C) - /g98*(T-25°C)²)/(K + /g103*(T-25°C)- /g100*(T-25°C)²) Hcorr is the humidity reading with the software correction algorithm for humidity already applied, as explained in the previous section. The function and values of the other parameters are explained in the table below. Name Function Value T Temperature at the time of humidity conversion (in °C) K Humidity sensor conversion constant 0.0307 /g97 Linear compensation, enumerator 0.0035/°C /g98 Quadratic compensation, enumerator 0.000043/°C² /g103 Linear compensation, denominator >15°C: 0.00001/°C /g100 Quadratic compensation, denominator 0.000002/°C² Numerical Temperature Compensation Example Sample Input Data Application of Correction Coefficients to Sample Reading T = 70°C Hcorr = 24.445%RH /g103 = 0.00001/°C + 0.00001 * 45 - 0.000002 * 45²) HTcorr = 30.291 % SOFTWARE SATURATION DRIFT COMPENSATION Capacitive humidity sensors read higher humidity values than the actual humidity level when they are exposed to a high-humidity environment for an extended time period. The DS1923’s humidity sensor produces readings that are higher than the actual humidity when exposed to humidity levels of about 70%RH and higher. This shift continues to increase while the device remains at 70%RH and above. This effect is called saturation drift, or sometimes referred to as hyteresis. This drift is reversible. Readings return to their regular level when the DS1923 is removed from a high-humidity environment. It is possible to compensate for most of the error introduced by the saturation drift by post-processing temperature and humidity logs using the equation below, which is based on laboratory tests and curve-fitting techniques. HScorr = HTcorr - /g83 k = 1 N 0.0156 * ARHk * 2.54 -0.3502*k ARHk The average software corrected and temperature compensated humidity reading of the k th hour that the device is continuously exposed to 70%RH or higher. Tk The average software corrected temperature reading of the k th hour that the device is continuously exposed to 70%RH or higher. N The number of hours that the device is continuously exposed to 70%RH or higher. HTcorr The humidity reading at the end of the N th hour with the software correction algorithm for humidity and temperature compensation already applied. See previous sections for details. The numbers in the equation are derived from curve fitting. They apply to a time scale in hours.

DS1923: Hygrochron Temperature/Humidity Logger iButton with 8kB Data Log Memory 52 of 52 Numerical Saturation Drift Compensation Example Sample Input Data (N = 8) Application of Correction Algorithm k (hour) T k (°C) ARH k (%RH) Partial Corrections (individual addends) 1 25.1 91.1 1.024321 2 25.0 92.5 0.751140 3 24.9 92.9 0.544824 4 25.0 93.1 0.393535 5 25.1 93.2 0.283950 6 25.1 93.3 0.205086 7 25.0 93.6 0.148591 8 24.9 93.7 0.107428 HTcorr = 93.70207 %RH Sum of partial corrections: 3.458875 HScorr = HTcorr - Sum of partial corrections = 93.70207 %RH - 3.458875%RH HScorr = 90.24319%RH The data in this example was taken from devices that were exposed for several hours to 90%RH at 25°C in a test chamber. The drift per hour decreases the longer the device is exposed to high humidity. The correction algorithm compensates for the drift reasonably well. Since the error introduced by the saturation is relatively small, for some applications compensation may not be necessary.