Datasheet

ManualsBrandsMaxim ManualsDigitalTemperature data logger

General Description

The DS1921G Thermochron

iButton

is a rugged, self-

sufficient system that measures temperature and records

the result in a protected memory section. The recording

is done at a user-defined rate, both as a direct storage of

temperature values as well as in the form of a histogram.

Up to 2048 temperature values taken at equidistant inter-

vals ranging from 1 to 255min can be stored. The his-

togram provides 63 data bins with a resolution of 2.0°C.

If the temperature leaves a user-programmable range,

the DS1921G also records when this happened, for how

long the temperature stayed outside the permitted range,

and if the temperature was too high or too low. An addi-

tional 512 bytes of battery-backed SRAM allow storing

information pertaining to the object to which the

DS1921G is associated. Data is transferred serially

through the 1-Wire

protocol, which requires only a sin-

gle data lead and a ground return. Every DS1921G is

factory lasered with a guaranteed unique, electrically

readable, 64-bit registration number that allows for abso-

lute traceability. The durable stainless steel package is

highly resistant to environmental hazards such as dirt,

moisture, and shock. Accessories permit the DS1921G

to be mounted on almost any object including contain-

ers, pallets, and bags.

Applications

Features

o Digital Thermometer Measures Temperature in

0.5°C Increments

o Accuracy ±1°C from -30°C to +70°C (See the

Electrical Characteristics

for Accuracy

Specification)

o Built-In Real-Time Clock (RTC) and Timer Has

Accuracy of ±2 Minutes per Month from 0°C to +45°C

o Water Resistant or Waterproof if Placed Inside

DS9107 i

Button Capsule (Exceeds Water

Resistant 3 ATM Requirements)

o Automatically Wakes Up and Measures Temperature

at User-Programmable Intervals from 1 Minute to

255 Minutes

o Logs Consecutive Temperature Measurements in

2KB of Data-Log Memory

o Records a Long-Term Temperature Histogram

with 2.0°C Resolution

o Programmable Temperature High and

Temperature Low Alarm Trip Points

o Records Up to 24 Timestamps and Durations

When Temperature Leaves the Range Specified

by the Trip Points

o 512 Bytes of General-Purpose Battery-Backed SRAM

o Communicates to Host with a Single Digital Signal

at 15.4kbps or 125kbps Using 1-Wire Protocol

Common iButton Features

o Digital Identification and Information by

Momentary Contact

o Unique, Factory-Lasered, and Tested 64-Bit

Registration Number (8-Bit Family Code + 48-Bit

Serial Number + 8-Bit CRC Tester) Assures

Absolute Traceability Because No Two Parts are

Alike

o Multidrop Controller for 1-Wire Net

o Chip-Based Data Carrier Compactly Stores Information

o Data Can Be Accessed While Affixed to Object

o Button Shape is Self-Aligning with Cup-Shaped

Probes

o Durable Stainless-Steel Case Engraved with

Registration Number Withstands Harsh

Environments

o Easily Affixed with Self-Stick Adhesive Backing,

Latched by Its Flange, or Locked with a Ring

Pressed Onto Its Rim

o Presence Detector Acknowledges When Reader

First Applies Voltage

o Meets UL 913, 5th Ed., Rev. 1997-02-24; Intrinsically

Safe Apparatus: Approved Under Entity Concept for

Use in Class I, Division 1, Group A, B, C, and D

Locations

DS1921G

Thermochron iButton

________________________________________________________________

Maxim Integrated Products

Ordering Information

19-5101; Rev 6; 3/12

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,

or visit Maxim’s website at www.maxim-ic.com.

PART TEMP RANGE PIN-PACKAGE

DS1921G-F5# -40°C to +85°C F5 i

Button

DS1921G-F5N# -40°C to +85°C F5 iButton

Examples of Accessories

PART ACCESSORY

DS9096P Self-Stick Adhesive Pad

DS9101 Multipurpose Clip

DS9093RA Mounting Lock Ring

DS9093A Snap-In Fob

DS9092 iButton Probe

Pin Configuration appears at end of data sheet.

Thermochron, i

Button, and 1-Wire are registered trademarks of

Maxim Integrated Products, Inc.

#Denotes a RoHS-compliant device that may include lead(Pb)

that is exempt under the RoHS requirements.

A NIST traceability certificate is available for the DS1921G-F5N.

See Application Note 4629 for details.

Temperature Logging in Cold Chain, Food Safety,

Pharmaceutical, and Medical Products

Summary of content (42 pages)

PAGE 1
9-5101; Rev 6; 3/12 Thermochron iButton Features The DS1921G Thermochron® iButton® is a rugged, self- o Digital Thermometer Measures Temperature in 0.
PAGE 2
DS1921G Thermochron iButton ABSOLUTE MAXIMUM RATINGS IO Voltage Range Relative to GND ..........................-0.5V to +6V IO Sink Current....................................................................20mA Operating Temperature Range ..........................-40°C to +85°C* Storage Temperature Range..............................-40°C to +50°C* *Storage or operation above +50°C significantly reduces battery life.
PAGE 3
Thermochron iButton (VPUP = +2.8V to +5.25V, TA = -40°C to +85°C.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS IO PIN: 1-Wire WRITE Standard speed 60 120 Overdrive speed, VPUP > 4.5V 6 15 Overdrive speed 8.
PAGE 4
DS1921G Thermochron iButton ELECTRICAL CHARACTERISTICS (continued) (VPUP = +2.8V to +5.25V, TA = -40°C to +85°C.) Note 17: WARNING: Not for use as the sole method of measuring or tracking temperature 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.
PAGE 5
Thermochron iButton 4 UPPER LIMIT RTC DEVIATION (MINUTES/MONTH) 2 0 LOWER LIMIT -2 -4 -6 -8 -10 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 TEMPERATURE (°C) Minimum Product Lifetime vs. Temperature at Different Sample Rates 11.00 10.00 MINIMUM PRODUCT LIFETIME (YEARS) 9.00 8.00 7.00 6.00 5.00 4.00 EVERY MINUTE NO SAMPLES EVERY 3 MINUTES OSCILLATOR OFF EVERY 10 MINUTES 3.00 2.00 1.00 0.
PAGE 6
Thermochron iButton DS1921G Minimum Product Lifetime vs. Sample Rate at Different Temperatures 11.00 +15°C 10.00 -20°C MINIMUM PRODUCT LIFETIME (YEARS) 9.00 -40°C 8.00 +40°C 7.00 +45°C 6.00 +50°C 5.00 +55°C 4.00 +60°C 3.00 2.00 +70°C 1.00 +85°C 0.00 1 10 100 1000 MINUTES BETWEEN SAMPLES Accuracy Limits 2.0 1.5 UPPER LIMIT 1.0 ACCURACY (°C) 0.5 0 -0.5 LOWER LIMIT -1.0 -1.5 -2.
PAGE 7
Thermochron iButton The DS1921G Thermochron iButton is an ideal device to monitor the temperature of any object it is attached to or shipped with, such as perishable goods or containers of temperature-sensitive chemicals. The general-purpose battery-backed SRAM can store an electronic copy of shipping information, date of manufacture and other important data written as clear as well as encrypted files. Note that the initial sealing level of the DS1921G achieves IP56.
PAGE 8
DS1921G Thermochron iButton histogram memory; and 2048 bytes of data-log memory. Except for the ROM and the scratchpad, all other memory is arranged in a single linear address space. All memory reserved for logging purposes, including counter registers and several other registers, is readonly for the user. The timekeeping and control registers are write protected while the device is programmed for a mission. The hierarchical structure of the 1-Wire protocol is shown in Figure 2.
PAGE 9
Thermochron iButton DS1921G MSB LSB 8-BIT CRC CODE MSB 8-BIT FAMILY CODE (21h) 48-BIT SERIAL NUMBER LSB MSB LSB MSB LSB Figure 3. 64-Bit Lasered ROM POLYNOMIAL = X8 + X5 + X4 + 1 1ST STAGE X0 2ND STAGE X1 3RD STAGE X2 4TH STAGE X3 5TH STAGE X4 6TH STAGE X5 7TH STAGE X6 8TH STAGE X7 X8 INPUT DATA Figure 4. 1-Wire CRC Generator 64-Bit Lasered ROM Each DS1921G contains a unique ROM code that is 64 bits long. The first 8 bits are a 1-Wire family code.
PAGE 10
DS1921G Thermochron iButton 32-BYTE INTERMEDIATE STORAGE SCRATCHPAD ADDRESS 0000h to 01FFh GENERAL-PURPOSE SRAM (16 PAGES) PAGES 0 to 15 0200h to 021Fh 32-BYTE REGISTER PAGE PAGE 16 0220h to 027Fh ALARM TIMESTAMPS AND DURATIONS PAGES 17 to 19 0280h to 07FFh (RESERVED FOR FUTURE EXTENSIONS) PAGES 20 to 63 0800h to 087Fh TEMPERATURE HISTOGRAM MEMORY PAGES 64 to 67 0880h to 0FFFh (RESERVED FOR FUTURE EXTENSIONS) PAGES 68 to 127 1000h to 17FFh DATA-LOG MEMORY (64 PAGES) PAGES128 to 191 180
PAGE 11
Thermochron iButton BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 0210h (No function, reads 00h) 0211h 0212h 0213h High Byte 0214h TCB BIT 2 BIT 1 BIT 0 FUNCTION ACCESS* — R R** Temperature Read-Out (Forced Conversion) Temperature R R** Low Byte Mission Start Delay R/W R/W** Status R/W R/W Mission Timestamp R R Mission Samples Counter R R Device Samples Counter R R MEMCLR MIP SIP 0 0215h Minutes 0216h Hours 0217h Date 0218h Month 0219h Year 021Ah Low Byte 021Bh Center
PAGE 12
DS1921G Thermochron iButton RTC and RTC Alarm Registers Map ADDRESS BIT 7 0200h 0 BIT 6 10 Seconds Single Seconds 0201h 0 10 Minutes Single Minutes 0202h 0 12/24 20 Hour AM/PM 10 Hour 0203h 0 0 0 0 0204h 0 0 0205h CENT 0 0206h BIT 5 BIT 4 BIT 3 BIT 1 BIT 0 Single Hours 0 10 Date 0 BIT 2 Day of Week Single Date 10 Months Single Months 10 Years Single Years 0207h MS 10 Seconds Alarm Single Seconds Alarm 0208h MM 10 Minutes Alarm Single Minutes Alarm 0209h MH
PAGE 13
Thermochron iButton ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 020Bh Temperature Low Alarm Threshold 020Ch Temperature High Alarm Threshold BIT 2 BIT 1 BIT 0 Sample Rate Register Map ADDRRESS BIT 7 BIT 6 BIT 5 020Dh BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 Sample Rate Temperature Conversion The DS1921G measures temperatures with a resolution of 0.5°C. Temperature values are represented in a single byte as an unsigned binary number, which translates into a theoretical range of 128°C.
PAGE 14
DS1921G Thermochron iButton Control Register Map ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 020Eh EOSC EMCLR 0 EM RO TLS THS TAS Control Register The DS1921G is set up for its operation by writing appropriate data to its special function registers that are located in the register page. Several functions that are controlled by a single bit only are combined into a single byte called the Control register (address 020Eh). This register can be read and written.
PAGE 15
Thermochron iButton ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0 0214h TCB MEMCLR MIP SIP 0 TLF THF TAF Status Register The Status register holds device status information and alarm flags. The register is located at address 0214h. Writing to this register does not necessarily end a mission. The functional assignments of the individual bits are explained below. The bits MIP, TLF, THF, and TAF can only be written to 0. All other bits are read-only. Bit 3 has no function.
PAGE 16
DS1921G Thermochron iButton Mission Timestamp Register Map ADDRESS BIT 7 0215h 0 BIT 6 0216h 0 12/24 0217h 0 0 0218h 0 0 BIT 5 BIT 4 BIT 3 10 Minutes 0219h 20 Hour AM/PM BIT 1 BIT 0 Single Minutes 10 Hour Single Hours 10 Date 0 BIT 2 Single Date 10 Months Single Months 10 Years Single Years Mission Samples Counter Register Map ADDRESS BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 021Ah Low Byte 021Bh Center Byte 021Ch High Byte BIT 2 BIT 1 BIT 0 Device Samples Counter Register
PAGE 17
Thermochron iButton TEMPERATURE EQUIVALENT IN °C 00h 01h HISTOGRAM BIN NUMBER HISTOGRAM BIN ADDRESS -40.0 or lower 0 800h to 801h -39.5 0 800h to 801h 02h -39.0 0 800h to 801h 03h -38.5 0 800h to 801h 04h -38.0 1 802h to 803h 05h -37.5 1 802h to 803h 06h -37.0 1 802h to 803h 07h -36.5 1 802h to 803h 08h -36.0 2 804h to 805h … … … … F3h +81.5 60 878h to 879h F4h +82.0 61 87Ah to 87Bh F5h +82.5 61 87Ah to 87Bh F6h +83.0 61 87Ah to 87Bh F7h +83.
PAGE 18
DS1921G Thermochron iButton ADDRESS DESCRIPTION 0220h Mission Samples Counter, Low Byte 0221h Mission Samples Counter, Center Byte 0222h Mission Samples Counter, High Byte ALARM EVENT Low Alarm 1 0223h Alarm Duration Counter 0224h to 0227h Alarm Timestamp and Duration Low Alarm 2 0228h to 024Fh Alarm Timestamp and Durations Low Alarms 3 to 12 0250h Mission Samples Counter, Low Byte 0251h Mission Samples Counter, Center Byte 0252h Mission Samples Counter, High Byte High Alarm 1 0253
PAGE 19
Thermochron iButton Address Registers and Transfer Status Because of the serial data transfer, the DS1921G employs three address registers, called TA1, TA2, and E/S (Figure 9). Registers TA1 and TA2 must be loaded with the target address to which the data is written or from which data is sent to the master upon a read command. Register E/S acts like a byte counter and transfer status register. It is used to verify data integrity with write commands.
PAGE 20
DS1921G Thermochron iButton BIT NUMBER 7 6 5 4 3 2 1 0 TARGET ADDRESS (TA1) T7 T6 T5 T4 T3 T2 T1 T0 TARGET ADDRESS (TA2) T15 T14 T13 T12 T11 T10 T9 T8 ENDING ADDRESS WITH DATA STATUS (E/S) (READ-ONLY) AA 0 PF E4 E3 E2 E1 E0 Figure 9. Address Registers write command was not recognized by the device. If everything went correctly, both flags are cleared and the ending offset indicates the address of the last byte written to the scratchpad.
PAGE 21
Thermochron iButton Copy Scratchpad [55h] This command is used to copy data from the scratchpad to the writable memory sections. Applying a Copy Scratchpad command to the Sample Rate register can start a mission provided that several preconditions are met. See the Mission Start and Logging Process section and the flowchart in Figure 11 for details.
PAGE 22
DS1921G Thermochron iButton FROM ROM FUNCTIONS FLOWCHART (FIGURE 13) MASTER Tx MEMORY OR CONTROL FUNCTION COMMAND 0Fh WRITE SCRATCHPAD? AAh READ SCRATCHPAD? N Y 55h COPY SCRATCHPAD N TO FIGURE 10b N Y Y DS1921G SETS EMCLR = 0 DS1921G SETS EMCLR = 0 DS1921G SETS EMCLR = 0 MASTER Tx TA1 [T7:T0], TA2 [T15:T8] MASTER Rx TA1 [T7:T0], TA2 [T15:T8] MASTER Tx TA1 [T7:T0], TA2 [T15:T8] DS1921G SETS SCRATCHPAD OFFSET = [T4:T0] AND CLEARS (PF, AA) MASTER Rx ENDING OFFSET WITH DATA STATUS (E/S) MAS
PAGE 23
Thermochron iButton F0h READ MEMORY? A5h READ MEMORY WITH CRC N DS1921G SETS EMCLR = 0 DS1921G SETS EMCLR = 0 DECISION MADE BY DS1921G EMCLR = 1? TO FIGURE 10c N Y MASTER Tx TA1 [T7:T0], TA2 [T15:T8] DS1921G SETS MEMORY ADDRESS = [T15:T0] N Y Y Y MASTER Rx TA1 [T7:T0], TA2 [T15:T8] 3Ch CLEAR MEMORY N DS1921G FROM FIGURE 10a DS1921G CLEARS MISSION TIMESTAMP, MISSION SAMPLES COUNTER, MISSION START DELAY, SAMPLE RATE REGISTER DS1921G SETS MEMORY ADDRESS = [T15:T0] DECISION MADE BY MASTER
PAGE 24
DS1921G Thermochron iButton FROM FIGURE 10b 44h CONVERT TEMPERATURE? N Y DS1921G SETS EMCLR = 0 Y MISSION IN PROGRESS? N TEMPERATURE CONVERSION PROCESS DS1921G SETS TCB = 0 DS1921G PERFORMS A TEMPERATURE CONVERSION DS1921G STARTS TEMPERATURE CONVERSION PROCESS DS1921G COPIES RESULT TO ADDRESS 0211h N MASTER Tx RESET? DS1921G SETS TCB = 1 Y END OF PROCESS N MASTER Tx RESET? Y TO FIGURE 10b Figure 10c.
PAGE 25
Thermochron iButton After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte address (TA1 = T[7:0], TA2 = T[15:8]) that indicates a starting byte location. With the subsequent read-data time slots, the master receives data from the DS1921G starting at the initial address and continues until the end of a 32-byte page is reached. At that point the bus master sends 16 additional read-data time slots and receives an inverted 16-bit CRC.
PAGE 26
DS1921G Thermochron iButton LOGGING PROCESS MISSION START PROCESS MIP = 1? N EM = 0? DS1921G COPIES RTC TO MISSION TIMESTAMP Y DS1921G SETS MIP = 0 DS1921G SETS DATA-LOG ADDRESS = 1000h N DS1921G MEASURES TEMPERATURE Y MEMCLR = 1? N DS1921G UPDATES HISTOGRAM, DEVICE SAMPLES COUNTER, MISSION SAMPLES COUNTER AND ALARM, IF APPLICABLE Y NEW SAMPLE RATE = 0? Y N N DS1921G COPIES NEW SAMPLE RATE FROM SCRATCHPAD TO SAMPLE RATE REGISTER Y Y RO = 1? DATA-LOG ADDRESS = 1800h? N DS1921G SETS MIP =
PAGE 27
Thermochron iButton a maximum data rate of 16.3kbps. The speed can be boosted to 142kbps by activating the overdrive mode. The DS1921G is not guaranteed to be fully compliant to the iButton standard. Its maximum data rate in standard speed is 15.4kbps and 125kbps in overdrive. The value of the pullup resistor primarily depends on the network size and load conditions. The DS1921G requires a pullup resistor of maximum 2.2kΩ at any speed. The idle state for the 1-Wire bus is high.
PAGE 28
DS1921G Thermochron iButton Initialization All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a reset pulse transmitted by the bus master, followed by presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the DS1921G is on the bus and is ready to operate. For more details, see the 1-Wire Signaling section.
PAGE 29
Thermochron iButton DS1921G MASTER Tx RESET PULSE FROM MEMORY/CONTROL FUNCTIONS FLOWCHART (FIGURE 10) FROM FIGURE 13b SHORT RESET PULSE? N OD = 0 Y MASTER Tx ROM FUNCTION COMMAND 33h READ ROM COMMAND? * N DS1921G Tx PRESENCE PULSE 55h MATCH ROM COMMAND? Y ** F0h SEARCH ROM COMMAND? N Y ECh CONDITIONAL SEARCH COMMAND? N Y N TO FIGURE 13b Y N CONDITION MET? Y DS1921G Tx FAMILY CODE (1 BYTE) DS1921G Tx BIT 0 * MASTER Tx BIT 0 DS1921G Tx BIT 0 * MASTER Tx BIT 0 BIT 0 MATCH? N
PAGE 30
DS1921G Thermochron iButton TO FIGURE 13a FROM FIGURE 13a CCh SKIP ROM COMMAND? N Y 3Ch OVERDRIVESKIP ROM? N 69h OVERDRIVEMATCH ROM? Y Y OD = 1 OD = 1 MASTER Tx RESET PULSE? Y N MASTER Tx BIT 0 *** N BIT 0 MATCH? N Y MASTER Tx BIT 1 BIT 1 MATCH? *** N Y MASTER Tx BIT 63 BIT 63 MATCH? FROM FIGURE 13a *** N Y TO FIGURE 13a ***ALWAYS TO BE TRANSMITTED AT OVERDRIVE SPEED. Figure 13b.
PAGE 31
Thermochron iButton standard speed at the next reset pulse of minimum 480µs duration. The Overdrive-Match ROM command can be used with a single or multiple devices on the bus. 1-Wire Signaling The DS1921G requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on one line: reset sequence with reset pulse and presence pulse, write-zero, write-one, and read-data. Except for the presence pulse, the bus master initiates all these signals.
PAGE 32
DS1921G Thermochron iButton A tRSTL duration of 480µs or longer exits the overdrive mode, returning the device to standard speed. If the DS1921G is in overdrive mode and tRSTL is no longer than 80µs, the device remains in overdrive mode. After the bus master has released the line, it goes into receive mode (Rx). Now the 1-Wire bus is pulled to V PUP through the pullup resistor or, in case of a DS2480B driver, through active circuitry.
PAGE 33
Thermochron iButton DS1921G WRITE-ONE TIME SLOT tW1L VPUP VIHMASTER VTH VTL VILMAX 0V ε tF tSLOT RESISTOR MASTER WRITE-ZERO TIME SLOT tW0L VPUP VIHMASTER VTH VTL VILMAX 0V ε tF tREC tSLOT RESISTOR MASTER READ-DATA TIME SLOT tMSR tRL VPUP VIHMASTER VTH MASTER SAMPLING WINDOW VTL VILMAX 0V δ tF tREC tSLOT RESISTOR MASTER DS1921G Figure 15.
PAGE 34
DS1921G Thermochron iButton With the Read Scratchpad command, the CRC is generated by first clearing the CRC generator and then shifting in the command code, the target addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target address. The DS1921G transmits this CRC only if the reading continues through the end of the scratchpad, regardless of the actual ending offset.
PAGE 35
Thermochron iButton SYMBOL DESCRIPTION <00 to EOP> Transfer of as many 00h bytes as are needed to reach a memory page boundary <32 bytes> Transfer of 32 bytes Transfer of an undetermined amount of data CRC-16 Transfer of an inverted CRC-16 FF loop Indefinite loop where the master reads FFh bytes AA loop Indefinite loop where the master reads AAh bytes 00 loop Indefinite loop where the master reads 00h bytes Command-Specific 1-Wire Communication Protocol—Color Codes Master-to-Slave S
PAGE 36
Thermochron iButton DS1921G 1-Wire Communication Examples (continued) Read Memory with CRC (Success) RST PD Select RMC TA CRC-16 <32 bytes> CRC-16 Loop The “32 bytes” are either valid page data or 00h bytes when reading reserved pages 20 through 63 or 68 through 127 or pages 192 and higher (beyond data-log memory). Read Memory with CRC (Invalid Address) RST PD Select RMC TA <00 to EOP> CRC-16 The “32 bytes” are all 00h.
PAGE 37
Thermochron iButton ADDRESS 200h 201h 202h 203h 204h 205h 206h DATA 00h 30h 15h 01h 81h 04h 02h With only a single DS1921G connected to the bus master, the communication of step 1 is as follows: MASTER MODE DATA (LSB FIRST) COMMENTS Tx (Reset) Rx (Presence) Reset pulse (480µs to 960µs) Tx CCh Issue Skip ROM command Tx 0Fh Issue Write Scratchpad command Tx 00h TA1, beginning offset = 00h Presence pulse Tx 02h Tx <7 data bytes> TA2, address = 0200h Tx (Reset) Rx (Pre
PAGE 38
DS1921G Thermochron iButton Step 2: Clear the data of the previous mission Set the EMCLR bit to 1, enable the RTC, and then execute the Clear Memory command. The RTC oscillator must be stable before the Clear Memory command is issued. Wait 500µs after issuing the Clear Memory command before proceeding to step 3.
PAGE 39
Thermochron iButton ADDRESS 20Eh 20Fh 210h 211h 212h 213h 214h DATA 02h 00h* 00h* 00h* 5Ah 00h 00h *Writing through address locations 20Fh to 211h is faster than accessing the Mission Start Delay register in a separate cycle. The write attempt has no effect on the contents of these registers.
PAGE 40
DS1921G Thermochron iButton Step 4: Set the temperature alarms and write the Sample Rate to start the mission In this example, the temperature alarms are set to -5°C for the low temperature threshold and 0°C for the high temperature threshold. The sample rate is once every 10min, allowing the mission to last up to 14 days.
PAGE 41
Thermochron iButton 5.89mm 0.51mm t o n ®. c 89 ® 21 YY 1-Wire® ® 50 om iB BRANDING ut Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. 16.
PAGE 42
DS1921G Thermochron iButton Revision History REVISION DATE DESCRIPTION PAGES CHANGED Added bullet “Water resistant or waterproof if placed inside DS9107 iButton capsule (Exceeds Water Resistant 3 ATM requirements)” Deleted “application pending” from UL bullet and safety statement Added text to Detailed Description section: Note that the initial sealing level of DS1921G achieves IP56.