DS1921 DALLAS [Dallas Semiconductor], DS1921 Datasheet



Manufacturer Part Number
High-Resolution Thermochron iButton
DALLAS [Dallas Semiconductor]

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Part Number
Part Number:
9 000
Part Number:
Part Number:
5 993
Part Number:
Part Number:
6 482
1-Wire, Microcan, and iButton are registered trademarks of Dallas Semiconductor.
Digital thermometer measures temperature in
1/8°C increments with ±1°C accuracy
Built-in real-time clock (RTC) and timer has
accuracy of 2 minutes per month from 0°C
to 45°C
Automatically wakes up and measures
temperature at user-programmable intervals
from 1 to 255 minutes
Logs up to 2048 consecutive temperature
measurements in protected nonvolatile (NV)
random access memory
Records a long-term temperature histogram
with 1/2°C resolution
Programmable temperature-high and
temperature-low alarm trip points
Records up to 24 time stamps and durations
when temperature leaves the range specified
by the trip points
512 bytes of general-purpose read/write NV
random access memory
Communicates to host with a single digital
signal at 15.4kbits or 125kbits per second
using 1-Wire
Fixed range: H: +15 C to +46°C;
Z: -5 C to +26°C
Digital identification and information by
momentary contact
Unique, factory-lasered and tested 64-bit reg-
istration number (8-bit family code + 48-bit
serial number + 8-bit CRC tester) assures ab-
solute traceability because no two parts are
Multidrop controller for 1-Wire net
Chip-based data carrier compactly stores
Data can be accessed while affixed to object
Button shape is self-aligning with cup-shaped
Range H: +15°C to +46°C; Z: -5°C to +26°C
1 of 44
High-Resolution Thermochron iButton
Durable stainless steel case engraved with
registration number withstands harsh
Easily affixed with self-stick adhesive
backing, latched by its flange, or locked with
a ring pressed onto its rim
Presence detector acknowledges when reader
first applies voltage
Meets UL#913 (4th Edit.). Intrinsically Safe
Apparatus: approved under Entity Concept
for use in Class I, Division 1, Group A, B, C,
and D Locations (application pending)
All dimensions are shown in millimeters.
+15 C to +46°C
-5 C to +26°C
Self-Stick Adhesive Pad
Multi-Purpose Clip
Mounting Lock Ring
Snap-In Fob
iButton Probe
F5 iButton
F5 iButton

Related parts for DS1921

DS1921 Summary of contents

Page 1

... All dimensions are shown in millimeters. ORDERING INFORMATION DS1921H-F5 + +46°C DS1921Z- +26°C EXAMPLES OF ACCESSORIES DS9096P Self-Stick Adhesive Pad DS9101 Multi-Purpose Clip DS9093RA Mounting Lock Ring DS9093A Snap-In Fob DS9092 iButton Probe DS1921H/Z 16.25 21 17.35 1-Wire Thermochron ® ® F5 iButton F5 iButton 051104 ...

Page 2

... The DS1921H has a fixed range of + +46°C. The DS1921Z has a fixed range +26°C. The high resolution makes the DS1921H and DS1921Z suitable for scientific research and development. The read/write NV memory can store information such as shipping manifests, dates of manufacture, or other relevant data written as ASCII or encrypted files ...

Page 3

... ROM may still be read normally. 64-BIT LASERED ROM Each DS1921 contains a unique ROM code that is 64 bits long. The first eight bits are a 1-Wire family code. The next 36 bits are a unique serial number. The next 12 bits, called temperature range code, allow distinguishing the DS1921H and DS1921Z from each other and from other DS1921 versions ...

Page 4

... SRAM, registers, flags All memory All memory Mission Time Stamp, Mission Samples Counter, Start Delay, Sample Rate, Alarm Time Stamps and Durations, Histogram Memory Memory address 211h LSB 8-Bit Family Code (21h) LSB MSB LSB HEX. EQUIVALENT 0010 4F2 0010 3B2 DS1921H/Z ...

Page 5

... X MEMORY The memory map of the DS1921H/Z is shown in Figure 5. The 4096-bit general-purpose SRAM make up pages 0 through 15. The timekeeping, control, and counter registers fill page 16, called Register Page (see Figure 6). Pages are assigned to storing the alarm time stamps and durations. The temperature histogram bins begin at page 64 and use up to four pages ...

Page 6

... DS1921H/Z REGISTER PAGE MAP Figure 6 ADDR b7 b6 0200h 0 10 Seconds 0201h 0 10 Minutes 0202h 0 12/24 AM/PM 0203h 0 0 0204h 0 0 0205h CENT 0 0206h 10 Years 0207h MS 10 Seconds Alarm 0208h MM 10 Minutes Alarm 0209h MH 12/24 020Ah MD 0 020Bh Temperature Low Alarm Threshold 020Ch Temperature High Alarm Threshold ...

Page 7

... 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 ( hours). To distinguish between the days of the week the DS1921H/Z includes a counter with a range from The assignment of counter value to the day of week is arbitrary. Typically, the number 1 is assigned to a Sunday (U ...

Page 8

... T[7… (° (DS1921Z) A value of 23°C, for example, thus translates into 68 decimal or 44h for the DS1921H, and 228 decimal or E4h for the DS1921Z. This corresponds to the binary patterns 0100 0100 and 1110 0100 respectively, which could be written to a Temperature Alarm Register (address 020Bh and 020Ch, respectively). ...

Page 9

... CONTROL REGISTER The DS1921H/Z 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 Control Register (address 20Eh). This register can be read and written. If the device is programmed for a mission, writing to the Control Register will end the mission and change the register contents ...

Page 10

... The maximum delay is 65535 minutes, equivalent to 45 days, 12 hours, and 15 minutes. For a typical mission, the Mission Start Delay mission is too long for a single DS1921H/Z to store all temperature readings at the selected sample rate, one can use several devices, staggering the Mission Start Delay to record the full period ...

Page 11

... This counter is reset through the Clear Memory command this bit reads 1 the DS1921H/Z has been set up for a mission and this mission is still in progress. A mission is started if the EM bit of the Control Register (address 20Eh and a non-zero value is written to the Sample Rate Register, address 20Dh ...

Page 12

... There are two alternatives to the way the DS1921H/Z will behave after the 2048 bytes of datalog memory is filled with data. With rollover disabled (RO = 0), the device will fill the datalog memory with the first 2048 mission samples ...

Page 13

... The DS1921H/Z can log high and low durations. The tolerance band is specified by means of the Temperature Alarm Threshold Registers, addresses 20Bh and 20Ch in the register page ...

Page 14

... This procedure is called missioning. First of all, DS1921H/Z needs to have its RTC set to valid time and date. This reference time may be UTC (also called GMT, Greenwich Mean Time) or any other time standard that was chosen for the application ...

Page 15

... The sample rate may be any value from 1 to 255, coded as an unsigned 8-bit binary number. As soon as the sample rate is written, the DS1921H/Z will set the MIP flag and clear the MEMCLR flag. After as many minutes as specified by the Mission Start Delay are over, the device will wait for the next minute boundary, then wake up, copy the current time and date to the Mission Time Stamp Register, and make the first temperature conversion of the mission ...

Page 16

... Only) WRITING WITH VERIFICATION To write data to the DS1921H/Z, the scratchpad has to be used as intermediate storage. First, the master issues the Write Scratchpad command to specify the desired target address, followed by the data to be written to the scratchpad. In the next step, the master sends the Read Scratchpad command to read the scratchpad and to verify data integrity ...

Page 17

... The ending offset/data status byte is unaffected. The hardware of the DS1921H/Z provides a means to accomplish error-free writing to the memory sec- tion. To safeguard data in the 1-Wire environment when reading and to simultaneously speed up data transfers recommended to packetize data into data packets of the size of one memory page each ...

Page 18

... Part Read Scratchpad N Y DS1921 sets EMCLR = 0 Master RX TA1 (T7:T0), TA2 (T15:T8) Master RX Ending Offset with Data Status (E/S) DS1921 sets Scratch- pad Offset = (T4:T0) Master RX Data Byte from Scratchpad Offset Y Master TX Reset? N Scratch- pad Offset = 11111b Master RX CRC16 of Command, Address Data, ...

Page 19

... Figure 10 F0H rd 3 Part Read Memory N Y DS1921 sets EMCLR = 0 Master TX TA1 (T7:T0), TA2 (T15:T8) DS1921 sets Memory Address = (T15:T0) Master RX Data Byte from Memory Address Master TX Reset End of Memory? Y Master RX "0"s From Figure Part DS1921H/Z ...

Page 20

... Decision made by DS1921 Decision made by Master To Figure Part A5H Read Mem. w/CRC Y DS1921 sets EMCLR = 0 Master TX TA1 (T7:T0), TA2 (T15:T8) DS1921 sets Memory Address = (T15:T0) Y End of Memory? N Master RX Master RX Data Byte 00 Byte from Memory Address Y Master TX Reset? N End of Page? Y Master RX CRC16 of ...

Page 21

... Part Clear Memory Y EMCLR = 1? Y DS1921 clears Mission Time Stamp, Mission Samples Counter, Mission Start Delay, Sample Rate Register DS1921 clears Alarm Time Stamps and Durations DS1921 clears Histogram Memory DS1921 sets MEMCLR = 1 DS1921 sets EMCLR = 0 N Master TX Reset Figure 10 ...

Page 22

... The command works essentially the same way as the simple Read Memory, except for the 16-bit CRC that the DS1921H/Z generates and transmits following the last data byte of a memory page. ...

Page 23

... Mission Start and Logging Process The DS1921H/Z does not use a special command to start a mission. Instead, a mission is started by writing a non-zero value to the Sample Rate Register using the Copy Scratchpad command. As shown in Figure 11, a new mission can only be started if the previous mission has been stopped (MIP = 0), the memory is cleared (MEMCLR = 1) and the mission is enabled ( ...

Page 24

... Note that the DS1921H/Z does not quite meet the full 16µs maximum low time of the normal 1-Wire bus Overdrive timing. With the DS1921H/Z the bus must be left low for no longer than 15µ ...

Page 25

... 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 DS1921H the bus and is ready to operate. For more details, see the 1-Wire Signaling section. ...

Page 26

... 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 will occur on the bus as multiple slaves transmit simultaneously (open drain pull-downs will produce a wired-AND result DS1921H/Z ...

Page 27

... From Figure Figure ECH N Cond. Search ROM Cond. Met DS1921 TX Bit DS1921 TX Bit Master TX Bit 0 N Bit 0 Match DS1921 TX Bit DS1921 TX Bit Master TX Bit 1 N Bit 1 Match ...

Page 28

... Part N CCH 3CH Skip Overdrive ROM? Skip ROM Master TX Reset Pulse? N Always to be transmitted at Overdrive speed 69H N N Overdrive Match Master TX Bit Bit 0 Match Master TX Bit 1 N Bit 1 Match? Y Master TX Bit Bit 63 Match? Y DS1921H/Z ...

Page 29

... The initialization sequence required to begin any communication with the DS1921H/Z is shown in Figure 14. A Reset Pulse followed by a Presence Pulse indicates the DS1921H/Z is ready to receive data, given the correct ROM and memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line for t longer will exit the Overdrive mode returning the device to standard speed ...

Page 30

... Wire devices. Read/Write Time Slots Data communication with the DS1921H/Z takes place in time slots that carry a single bit each. Write time slots transport data from bus master to slave. Read time-slots transfer data from slave to master. The definitions of the write and read time slots are illustrated in Figure 15. ...

Page 31

... DS1921H/Z will start pulling the data line low; its internal timing generator determines when this pull- down ends and the voltage starts rising again. When responding with a 1, the DS1921H/Z will not hold the data line low at all, and the voltage starts rising as soon as t ...

Page 32

... With the Write 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 and all the data bytes. The DS1921H/Z will transmit this CRC only if the data bytes written to the scratchpad include scratchpad ending offset 11111b ...

Page 33


Page 34

... The "32 bytes" are either valid page data or 00h bytes when reading reserved pages 20 through through 127 or pages 192 and higher (beyond datalog memory). TA <data to EOS> CRC16\ TA <data> RST PD TA-E/S <data to EOS> CRC16\ TA-E/S AA loop TA-E/S FF loop TA <data to EOM> 00 loop TA 00 loop TA <data to EOP> CRC16 DS1921H/Z FF loop FF loop <32 bytes> CRC16\ Loop ...

Page 35

... Select CT To read the result and to verify success, read the addresses 0211h (result) and the Device Samples Coun??ter at address 021Dh to 021Fh. If the count has incremented, the command was executed successfully. TA <00 to EOP> CRC16\ FF loop FF loop DS1921H/Z <32 bytes> CRC16\ Loop ...

Page 36

... Assumption: The previous mission has come to an end. To end an ongoing mission write the MIP bit in the Status Register to 0. The preparation of a DS1921H/Z for a mission including the start of the mission requires up to four steps: Step 1: set the RTC (if it needs to be adjusted) ...

Page 37

... Clear Memory command is issued. Wait 500 µs after issuing the Clear Memory command before proceeding to Step 3. This results in the following data to be written to the Status Register: Address: 20Eh Data: 40h With only a single DS1921H/Z connected to the bus master, the communication of step follows: MASTER MODE ...

Page 38

... 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. With only a single DS1921H/Z connected to the bus master, the communication of step follows: MASTER MODE ...

Page 39

... DS1921Z device. The sample rate is once every 10 minutes, allowing the mission to last days. This results in the following data to be written to the special function registers: Address: 20Bh 20Ch Data: 2Ch With only a single DS1921H/Z connected to the bus master, the communication of step follows: MASTER MODE ...

Page 40

... Safety ABSOLUTE MAXIMUM RATINGS* IO Voltage to GND IO Sink Current Temperature Range DS1921H, DS1921Z Storage Temperature Range * 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. ...

Page 41

... -48 +46 PPM 15 46 °C -5 +26 75 360 ms 130 °C (see graphs) — whenever the master drives the line low. DS1921H 17, 18 14, 16 ...

Page 42

... DS1921H/Z Values Standard Speed Overdrive Speed min max min 1) 1) 65µs (undef.) 8µs 540µs 640µs 48µs 15µs 60µs 1.1µs 60µs 270µ ...

Page 43

... Minimum Product Lifetime vs Temperature at Different Sample Rates Every Minute No Samples 11.00 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 0.00 -40 -30 -20 -10 Lower Limit Upper Limit Temperature (°C) Every 3 Min. Every 10 Min. Osc. Off Temperature (° DS1921H/Z ...

Page 44

... Minimum Product Lifetime vs Sample Rate at Different Temperatures -5°C 12.00 11.00 10.00 9.00 8.00 7.00 6.00 5.00 4.00 3.00 2.00 1.00 1 Minutes between Samples 15 °C 26°C 37°C 10 100 46°C 1000 DS1921H/Z ...

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