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DS1921Z
High Resolution Thermochron iButton Range H: +15°C to +46°C; Z: -5°C to +26°C
SPECIAL FEATURES 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 Water resistant or waterproof if placed inside DS9107 iButton® capsule (Exceeds Water Resistant 3 ATM requirements) Automatically wakes up and measures temperature at user-programmable intervals from 1 to 255 minutes Logs consecutive temperature measurements in 2KB of datalog 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 battery-backed SRAM Communicates to host with a single digital signal at 15.4kbits or 125kbits per second using 1-Wire® protocol Fixed range: H: +15°C to +46°C; Z: -5°C to +26°C
COMMON iButton DEVICE FEATURES Digital identification and information by momentary contact 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 Multidrop controller for 1-Wire net Chip-based data carrier compactly stores information Button shape is self-aligning with cup-shaped probes Durable stainless steel case engraved with registration number withstands harsh environments Easily affixed with self-stick adhesive backing, latched by its flange, or locked with a ring pressed onto its rim Presence detector acknowledges when reader first applies voltage
PIN CONFIGURATION IO GND
0.51
5.89
16.25
17.35 D6 21 3B2000FBC52B 1-Wire
Thermochron® All dimensions are shown in millimeters.
ORDERING INFORMATION PART TEMP RANGE PIN-PACKAGE DS1921H-F5# +15°C to +46°C F5 Can
DS1921Z-F5# -5°C to +26°C F5 Can
#Denotes a RoHS-compliant device that may include lead(Pb) that is exempt under the RoHS requirements.
EXAMPLES OF ACCESSORIES DS9096P Self-Stick Adhesive Pad DS9101 Multi-Purpose Clip DS9093RA Mounting Lock Ring DS9093A Snap-In Fob DS9092 iButton Device Probe
DS1921H/DS1921Z High-Resolution Thermochron iButton Devices
DS1921H/Z
iButton DEVICE DESCRIPTION The DS1921H/Z Thermochron® iButton devices are rugged, self-sufficient systems that measure temperature and record 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 intervals ranging from 1 to 255 minutes can be stored. The histogram provides 64 data bins with a resolution of 0.5°C. If the temperature leaves a user-programmable range, the DS1921H/Z will also record when this happened, for how long the temperature stayed outside the permitted range, and if the temperature was too high or too low. Additional 512 bytes of general-purpose battery-backed SRAM allow storing information pertaining to the object to which the DS1921H/Z is associated. Data is transferred serially via the 1-Wire protocol, which requires only a single data lead and a ground return. Every DS1921H/Z is factory-lasered with a guaranteed unique electrically readable 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 DS1921H/Z to be mounted on almost any object, including containers, pallets, and bags.
APPLICATION The DS1921Z is an ideal device to monitor the temperature of any object it is attached to or shipped with, such as fresh produce, medical drugs and supplies. It is also ideal for use in refrigerators. The DS1921H is intended for monitoring the body temperature of humans and animals and for monitoring temperature critical processes such as curing, powder coating, and painting. Alternatively, the DS1921H can be used for monitoring the temperature of clean rooms, and computer and equipment rooms. It can also aid in calculating the proportional share of heating cost of each party in buildings with central heating. The DS1921H has a fixed range of +15°C to +46°C. The DS1921Z has a fixed range of -5°C to +26°C. The high resolution makes the DS1921H and DS1921Z suitable for scientific research and development. The general-purpose battery-backed SRAM can store information such as shipping manifests, dates of manufacture, or other relevant data written as ASCII or encrypted files. Note that the initial sealing level of DS1921H/Z achieves the equivalent of IP56. Aging and use conditions can degrade the integrity of the seal over time, so for applications with significant exposure to liquids, sprays, or other similar environments, it is recommended to place the Thermochron in the DS9107 iButton capsule. The DS9107 provides a watertight enclosure that has been rated to IP68 (refer to Application Note 4126).
OVERVIEW The block diagram in Figure 1 shows the relationships between the major control and memory sections of the DS1921H/Z. The device has seven main data components: 1) 64-bit lasered ROM; 2) 256-bit scratchpad; 3) 4096-bit general-purpose SRAM; 4) 256-bit register page of timekeeping, control, and counter registers; 5) 96 bytes of alarm time stamp and duration logging memory; 6) 128 bytes of histogram memory; and 7) 2048 bytes of datalog 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, counter registers and several other registers are read-only 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. The bus master must first provide one of the seven ROM function commands: 1) Read ROM; 2) Match ROM; 3) Search ROM; 4) Conditional Search ROM; 5) Skip ROM; 6) Overdrive-Skip ROM; or 7) Overdrive-Match ROM. Upon completion of an Overdrive ROM command byte executed at standard speed, the device will enter Overdrive mode, where all subsequent communication occurs at a higher speed. The protocol required for these ROM function commands is described in Figure 13. After a ROM function command is successfully executed, the memory functions become accessible and the master may provide any one of
DS1921H/Z
DS1921H/Z BLOCK DIAGRAM Figure 1 InternalTimekeeping &Control Reg. &Counters
3V Lithium
General-PurposeSRAM
Register Page
Alarm Time Stampand DurationLogging Memory
DatalogMemory
Histogram Memory
32.768kHzOscillator
ControlLogicTemperatureSensor
256-BitScratchpad
MemoryFunctionControl
ROMFunctionControl
64-BitLaseredROM
ParasitePoweredCircuitry
1-WirePortIO
PARASITE POWER The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the IO input is high. IO will provide sufficient power as long as the specified timing and voltage requirements are met. The advantages of parasite power are two-fold: 1) By parasiting off this input, battery power is not consumed for 1-Wire ROM function commands, and 2) if the battery is exhausted for any reason, the ROM may still be read normally. The remaining circuitry of the DS1921 is solely operated by battery energy. As a consequence, if the battery is exhausted, all memory data is lost including the data of the last mission, and no new mission can be started. Application Note 5057: OneWireViewer Tips and Tricks explains how to check the battery status.
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. The last eight bits are a CRC of the first 56 bits. See Figure 3 for details. The 1-Wire CRC is generated using a polynomial generator consisting of a shift register and XOR gates as shown in Figure 4. The polynomial is X8 + X5 + X4 + 1. Additional information about the Maxim 1-Wire Cyclic Redundancy Check is available in Application Note 27. The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a time is shifted in. After the eighth bit of the family code has been entered, then the serial
DS1921H/Z
HIERARCHICAL STRUCTURE FOR 1-Wire PROTOCOL Figure 2 1-Wire netOtherDevicesBusMaster
CommandLevel:
1-Wire ROM FunctionCommands
DS1921-SpecificMemory/ControlFunction Commands
DS1921AvailableCommands:
Read ROMMatch ROMSearch ROMSkip ROMOverdrive SkipOverdrive MatchConditional Search ROM
Write ScratchpadRead ScratchpadCopy ScratchpadRead MemoryRead Memory w/CRCClear Memory
Convert Temperature
Data FieldAffected:
64-bit Reg. #64-bit Reg. #64-bit Reg. #N/AOD-Flag64-bit Reg. #, OD-Flag64-bit Reg. #, Cond. Search settings, device status
256-bit scratchpad, flags256-bit scratchpad4096-bit SRAM, registers, flagsAll memoryAll memoryMission Time Stamp, Mission SamplesCounter, Start Delay, Sample Rate, Alarm Time Stamps and Durations, Histogram MemoryMemory address 211h
Cmd.Codes:
33h55hF0hCCh3Ch69hECh
0FhAAh55hF0hA5h3Ch
44h
64-BIT LASERED ROM Figure 3 MSB LSB
8-Bit CRC Code 12-Bit Temperature Range Code 36-Bit Serial Number 8-Bit Family Code (21h)
MSB LSB MSB LSB MSB LSB MSB LSB
DEVICE TEMP. RANGE (°C) RESOLUTION (°C) TEMP. RANGE CODE HEX. EQUIVALENT DS1921H-F5 +15 to +46 0.125 0100 1111 0010 4F2
DS1921Z-F5 -5 to +26 0.125 0011 1011 0010 3B2
DS1921H/Z
1-Wire CRC GENERATOR Figure 4 0X1X2X3X4X5X6X7X8
Polynomial = X8 + X5 + X4 + 1st
STAGE2nd
STAGE3rd
STAGE4th
STAGE6th
STAGE5th
STAGE7th
STAGE8th
STAGE
INPUT DATA
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 17 to 19 are assigned to storing the alarm time stamps and durations. The temperature histogram bins begin at page 64 and use up to four pages. The datalog memory covers pages 128 to 191. Memory pages 20 to 63, 68 to 127, and 192 to 255 are reserved for future extensions. The scratchpad is an additional page that acts as a buffer when writing to the SRAM or the register page. The memory pages 17 and higher are read-only for the user. They are written to or erased solely under supervision of the on-chip control logic.
DS1921H/Z MEMORY MAP Figure 5 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 Time Stamps 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
Datalog Memory (64 Pages) Pages 128 to 191
1800h to 1FFFh (Reserved for Future Extensions) Pages 192 to 255
DS1921H/Z
DS1921H/Z REGISTER PAGE MAP Figure 6
ADDR b7 b6 b5 b4 b3 b2 b1 b0 Function Access* 0200h 0 10 Seconds Single Seconds
0201h 0 10 Minutes Single Minutes Real-
0202h 0 12/24 20h. AM/PM 10h. Single Hours Time Clock R/W; R/W**
0203h 0 0 0 0 0 Day of Week Registers
0204h 0 0 10 Date Single Date
0205h CENT 0 0 10m. Single Months
0206h 10 Years Single Years
0207h MS 10 Seconds Alarm Single Seconds Alarm Real-
0208h MM 10 Minutes Alarm Single Minutes Alarm Time
0209h MH 12/24 10ha. A/P 10h. alm. Single Hours Alarm Clock Alarm R/W; R/W**
020Ah MD 0 0 0 0 Day of Week Alarm Registers
020Bh Temperature Low Alarm Threshold Temp. R/W; R/W** 020Ch Temperature High Alarm Threshold Alarms 020Dh Number of Minutes Between Temperature Conversions Sample Rate R/W; R**
020Eh EOSC EMCLR 0 EM RO TLS THS TAS Control R/W; R/W**
020Fh (no function, reads 00h) (N/A) R; R** 0210h (no function, reads 00h) (N/A) R; R** 0211h Temperature Read Out (Forced Conversion) Temp. R; R** 0212h Low Byte Start R/W; R/W** 0213h High Byte Delay 0214h TCB MEMCLR MIP SIP 0 TLF THF TAF Status R/W; R/W
0215h Minutes
0216h Hours Mission
0217h Date Time R; R
0218h Month Stamp
0219h Year
021Ah Low Byte Mission
021Bh Center Byte Samples R; R
021Ch High Byte Counter
021Dh Low Byte Device
021Eh Center Byte Samples R; R
021Fh High Byte Counter *The first entry in column ACCESS is valid between missions. The second entry shows the applicable access mode while a mission is in progress. **While a mission is in progress, these addresses can be read. The first attempt to write to these registers (even read-only ones), however, will end the mission and overwrite selected writeable registers.
TIMEKEEPING The RTC/alarm and calendar information is accessed by reading/writing the appropriate bytes in the register page, address 200h to 206h. Note that some bits are set to 0. These bits will always read 0 regardless of how they are written. The contents of the time, calendar, and alarm registers are in the
DS1921H/Z
RTC 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 0 0 0 Day of Week
0204h 0 0 10 Date Single Date
0205h CENT 0 0 10m. Single Months
0206h 10 Years Single Years
0207h MS 10 Seconds Alarm Single Seconds Alarm
0208h MM 10 Minutes Alarm Single Minutes Alarm
0209h MH 12/24 10ha. A/P 10h. alm. Single Hours Alarm
020Ah MD 0 0 0 0 Day of Week Alarm
RTC/Calendar The RTC of the DS1921H/Z 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). To distinguish between the days of the week the DS1921H/Z includes a counter with a range from 1 to 7. The assignment of counter value to the day of week is arbitrary. Typically, the number 1 is assigned to a Sunday (U.S. standard) or to a Monday (European standard). 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. The DS1921H/Z is Y2K-compliant. Bit 7 (CENT) of the Months Register at address 205h serves as a century flag. When the Year Register rolls over from 99 to 00 the century flag will toggle. It is recommended to write the century bit to a 1 when setting the RTC to a time/date between the years 2000 and 2099.
RTC Alarms The DS1921H/Z also contains a RTC alarm function. The alarm registers are located in registers 207h to 20Ah. The most significant bit of each of the alarm registers is a mask bit. When all of the mask bits are logic 0, an alarm will occur once per week when the values stored in timekeeping registers 200h to 203h match the values stored in the time of day alarm registers. Any alarm will set the Timer Alarm Flag (TAF) in the device's Status Register (address 214h). The bus master may set the Search Conditions in the Control Register (address 20Eh) to identify devices with timer alarms by means of the Conditional Search function (see ROM Function Commands).
DS1921H/Z
RTC Alarm Control
ALARM REGISTER MASK BITS (Bit 7 of 207h to 20Ah)
MS MM MH MD 1 1 1 Alarm once per second. 1 1 1 Alarm when seconds match (once per minute). 0 1 1 Alarm when minutes and seconds match (once every hour). 0 0 1 Alarm when hours, minutes and seconds match (once every day). 0 0 0 Alarm when day, hours, minutes, and seconds match (once every week).
TEMPERATURE CONVERSION The DS1921H and DS1921Z measure temperatures with a resolution of 1/8th of a degree Celsius. Temperature values are represented in a single byte as an unsigned binary number, which translates into a range of 32°C. The possible values are 0000 0000 (00h) through 1111 1111 (FFh). The codes 01h to FEh are considered valid temperature readings. Since the DS1921H and DS1921Z have different starting temperatures, the meaning of a binary temperature code depends on the device. If a temperature conversion yields a temperature that is out-of-range, it will be recorded as 00h (if too low) or FFh (if too high). Since out-of-range results are accumulated in histogram bins 0 and 63 the data in these bins is of limited value (see the Temperature Logging and Histogram section). For this reason the specified temperature range of the DS1921H and DS1921Z is considered to begin at code 04h and end at code FBh, which corresponds to histogram bins 1 to 62. With T[7..0] representing the decimal equivalent of a temperature reading, the temperature value is calculated as ϑ (°C) = T[7…0] / 8 + 14.500 (DS1921H) ϑ (°C) = T[7…0] / 8 - 5.500 (DS1921Z) This equation is valid for converting temperature readings stored in the datalog memory as well as for data read from the forced temperature conversion readout Register (address 211h). To specify the high or low temperature alarm thresholds, this equation needs to be resolved to T[7…0] = 8 * ϑ (°C) -116 (DS1921H) T[7…0] = 8 * ϑ (°C) + 44 (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).
Temperature Alarm Register Map ADDR b7 b6 b5 b4 b3 b2 b1 b0
DS1921H/Z
SAMPLE RATE The content of the Sample Rate Register (address 020Dh) determines how many minutes the temperature conversions are apart from each other during a mission. The sample rate may be any value from 1 to 255, coded as an unsigned 8-bit binary number. If the memory has been cleared (Status Register bit MEMCLR = 1) and a mission is enabled (Status Register bit EM = 0), writing a non-zero value to the Sample Rate Register will start a mission. For a full description of the correct sequence of steps to start a temperature-logging mission see sections Missioning or Missioning Example.
Sample Rate Register Map ADDR b7 b6 b5 b4 b3 b2 b1 b0 020Dh Sample Rate
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.
Control Register Bitmap ADDR b7 b6 b5 b4 b3 b2 b1 b0
020Eh EOSC EMCLR 0 EM RO TLS THS TAS
The functional assignments of the individual bits are explained in the table below. Bit 5 has no function. It always reads 0 and cannot be written to 1.
Control Register Details
BIT DESCRIPTION BIT(S) DEFINITION EOSC: Enable Oscillator b7 This bit controls the crystal oscillator of the RTC. When set to logic 0, the oscillator will start operation. When written to logic 1, the oscillator will stop and the device is in a low-power data retention mode. This bit
must be 0 for normal operation. The RTC must have advanced at least 1 second before a mission start will be accepted.
EMCLR: Memory Clear Enable b6 This bit needs to be set to logic 1 to enable the Clear Memory function, which is invoked as a memory function command. The Time-Stamp, Histogram Memory as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay and Sample Rate will be cleared only if the Clear Memory command is issued with the next access to
the device. The EMCLR bit will return to 0 as the next memory function command is executed.
EM: Enable Mission b4 This bit controls whether the DS1921H/Z will begin a mission as soon as the sample rate is written. To enable the device for a mission, this bit must be 0.
RO: Rollover Enable/Disable b3 This bit controls whether the datalog memory is overwritten with new data or whether data logging is stopped once the memory is filled with data during a mission. Setting this bit to a 1 enables the rollover and data logging continues at the beginning overwriting previously collected data. Clearing this bit to 0 disables the rollover and no further temperature values will be stored in the datalog memory once it is filled with data. This will not stop the mission. The device will continue
DS1921H/Z
BIT DESCRIPTION BIT(S) DEFINITION TLS: Temperature Low Alarm Search b2 If this bit is 1, the device will respond to a Conditional Search command if during a mission the temperature has reached or is lower than the Low Temperature Threshold stored at address 020Bh.
THS: Temperature High Alarm Search b1 If this bit is 1, the device will respond to a Conditional Search command if during a mission the temperature has reached or is higher than the High Temperature Threshold stored at address 020Ch.
TAS: Timer Alarm Search b0 If this bit is 1, the device will respond to a Conditional Search command if during a mission a timer alarm has occurred. Since a timer alarm cannot be disabled, the TAF flag usually reads 1 during a mission. Therefore it may be advisable to set the TAS bit to a 0, in most cases.
Mission Start Delay Counter The content of the Mission Start Delay Counter determines how many minutes the device will wait before starting the logging process. The mission start delay value is stored as unsigned 16-bit integer number at addresses 212h (low byte) and 213h (high byte). The maximum delay is 65535 minutes, equivalent to 45 days, 12 hours, and 15 minutes. For a typical mission, the Mission Start Delay is 0. If a 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. In this case, the RO bit in the control register (address 020Eh) must be set to 0 to prevent overwriting of the recorded temperature log after the datalog memory is full. See Mission Start and Logging Process description and flow chart for details.
Status Register The Status Register holds device status information and alarm flags. The register is located at address 214h. Writing to this register will not necessarily end a mission.
Status Register Bitmap ADDR b7 b6 b5 b4 b3 b2 b1 b0
0214h TCB MEMCLR MIP SIP 0 TLF THF TAF
The functional assignments of the individual bits are explained in the table 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.
Status Register Details
BIT DESCRIPTION BIT(S) DEFINITION TCB: Temperature Core Busy b7 If this bit reads 0 the DS1921H/Z is currently performing a temperature conversion, either self-initiated because of a mission being in progress or initiated by a command when a mission is not in progress. The TCB bit goes low just before a conversion starts and returns to high just after the result is latched into the readout register at address 0211h.
MEMCLR: Memory Cleared b6 If this bit reads 1, the memory pages 17 and higher (alarm time stamps/durations, temperature histogram, excluding datalog memory), as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay and Sample Rate have been cleared to 0 from executing a Clear Memory function command. The MEMCLR bit will return to 0 as soon as writing a non-0 value to the Sample Rate Register starts a new mission, provided that the EM bit is also 0. The memory has to be
DS1921H/Z
BIT DESCRIPTION BIT(S) DEFINITION MIP: Mission in Progress b5 If 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) is 0 and a non-zero value is written to the Sample Rate Register, address 20Dh. The MIP bit returns from logic 1 to logic 0 when a mission is ended. A mission will end with the first write attempt (Copy Scratchpad command) to any register in the address range of 200h to 213h. Alternatively, a mission can be ended by directly writing to the Status Register and setting the MIP bit to 0. The MIP bit cannot be set to 1 by writing to the status register.
SIP: Sample in Progress b4 If this bit reads 1 the DS1921H/Z is currently performing a temperature conversion as part of a mission in progress. The mission samples occur on the seconds rollover from 59 to 00. The SIP bit will change from 0 to 1 approximately 250ms before the actual temperature conversion begins allowing the circuitry of the chip to wake-up. A temperature conversion including a wake-up phase takes maximum 875ms. During this time read accesses to the memory pages 17 and higher are permissible but may reveal invalid data.
TLF: Temperature Low Flag b2 Logic 1 in the Temperature Low Flag bit indicates that a temperature measurement during a mission revealed a temperature equal to or lower than the value in the Temperature Low Threshold Register. The Temperature Low Flag can be cleared at any time by writing this bit to 0. This flag must be cleared before starting a new mission.
THF: Temperature High Flag b1 Logic 1 in the Temperature High Flag bit indicates that a temperature measurement during a mission revealed a temperature equal to or higher than the value in the Temperature High Threshold Register. The Temperature High Flag can be cleared at any time by writing this bit to 0. This flag must be cleared before starting a new mission.
TAF: Timer Alarm Flag b0 If this bit reads 1, a RTC alarm has occurred (see section TIMEKEEPING for details). The Timer Alarm Flag can be cleared at any time by writing this bit to logic 0. Since the timer alarm cannot be disabled, the TAF flag usually reads 1 during a mission. This flag should be cleared before starting a new mission.
MISSION TIME STAMP The Mission Time Stamp indicates the time and date of the first temperature conversion of a mission. Subsequent temperature conversions will take place as many minutes apart from each other as specified by the value in the Sample Rate Register. Mission samples occur on minute boundaries.
Mission Time Stamp Register Bitmap ADDR b7 b6 b5 b4 b3 b2 b1 b0 0215h 0 10 Minutes Single Minutes
0216h 0 12/24 20h. AM/PM 10h. Single Hours
0217h 0 0 10 Date Single Date 0218h 0 0 0 10m. Single Months 0219h 10 Years Single Years
MISSION SAMPLES COUNTER The Mission Samples Counter indicates how many temperature measurements have taken place during the current mission in progress (if MIP = 1) or during the latest mission (if MIP = 0). The value is stored
DS1921H/Z
Mission Samples Counter Register Map ADDR b7 b6 b5 b4 b3 b2 b1 b0 021Ah Low Byte 021Bh Center Byte 021Ch High Byte
DEVICE SAMPLES COUNTER The Device Samples Counter indicates how many temperature measurements have taken place since the device was assembled at the factory. The value is stored as an unsigned 24-bit integer number. The maximum number that can be represented in this format is 16777215, which is higher than the expected lifetime of the DS1921H/Z devices. This counter cannot be reset under software control.
Device Samples Counter Register Map ADDR b7 b6 b5 b4 b3 b2 b1 b0 021Dh Low Byte 021Eh Center Byte 021Fh High Byte
TEMPERATURE LOGGING AND HISTOGRAM Once setup for a mission, the DS1921H/Z logs the temperature measurements simultaneously byte after byte in the datalog memory as well as in histogram form in the histogram memory. The datalog memory is able to store 2048 temperature values measured at equidistant time points. The first temperature value of a mission is written to address location 1000h of the datalog memory, the second value to address location 1001h and so on. Knowing the starting time point (Mission Time Stamp), the interval between temperature measurements, the Mission Samples Counter, and the rollover setting, one can reconstruct the time and date of each measurement stored in the datalog. 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. Additional mission samples are not logged in the datalog, but the histogram, and temperature alarm memory continue to update. With rollover enabled (RO = 1), the datalog will wrap around, and overwrite previous data starting at 1000h for the every 2049th mission sample. In this mode the device stores the last 2048 mission samples. For the temperature histogram, the DS1921H/Z provides 64 bins that begin at memory address 0800h. Each bin consists of a 16-bit, non-rolling-over binary counter that is incremented each time a temperature value acquired during a mission falls into the range of the bin. The least significant byte of each bin is stored at the lower address. Bin 0 begins at memory address 0800h, bin 1 at 0802h, and so on up to 087Eh for bin 63, as shown in Figure 7. The number of the bin to be updated after a temperature conversion is determined by cutting off the two least significant bits of the binary temperature value. Out of range values are range locked and counted as 00h or FFh.
DS1921H/Z
HISTOGRAM BIN AND TEMPERATURE CROSS-REFERENCE Figure 7
TEMPERATURE READING DS1921H TEMP. EQUIV. IN °C DS1921Z TEMP. EQUIV. IN °C HISTOGRAM BIN NUMBER HISTOGRAM BIN ADDRESS 00h
14.500 -5.500 0 800h to 801h
01h
14.625 -5.375 0 800h to 801h
02h
14.750 -5.250 0 800h to 801h
03h
14.875 -5.125 0 800h to 801h
04h 15.000 -5.000 1 802h to 803h
05h 15.125 -4.875 1 802h to 803h
06h 15.250 -4.750 1 802h to 803h
07h 15.375 -4.625 1 802h to 803h
08h 15.500 -4.500 2 804h to 805h
F7h 45.375 25.375 61 87Ah to 87Bh
F8h 45.500 25.500 62 87Ch to 87Dh
F9h 45.625 25.625 62 87Ch to 87Dh
FAh 45.750 25.750 62 87Ch to 87Dh
FBh 45.875 25.875 62 87Ch to 87Dh
FCh
46.000 26.000 63 87Eh to 87Fh
FDh
46.125 26.125 63 87Eh to 87Fh
FEh
46.250 26.250 63 87Eh to 87Fh
FFh
46.375 26.375 63 87Eh to 87Fh Since each data bin is 2 bytes it can increment up to 65535 times. Additional measurements for a bin that has already reached its maximum value will not be counted; the bin counter will remain at its maximum value. With the fastest sample rate of one sample every minute, a 2-byte bin is sufficient for up to 45 days if all temperature readings fall into the same bin.
TEMPERATURE ALARM LOGGING For some applications it may be essential to not only record temperature over time and the temperature histogram, but also record when exactly the temperature has exceeded a predefined tolerance band and for how long the temperature stayed outside the desirable range. 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. One can set a high and a low temperature threshold. See section Temperature Conversion for the data format the temperature has to be written in. As long as the temperature values stay within the tolerance band (i.e., are higher than the low threshold and lower than the high threshold), the DS1921H/Z will not record any temperature alarm. If the temperature during a mission reaches or exceeds either threshold, the DS1921H/Z will generate an alarm and set either the Temperature High Flag (THF) or the Temperature Low Flag (TLF) in the Status Register (address 214h). This way, if the search conditions (address 20Eh) are set accordingly, the master can quickly identify devices with temperature alarms by means of the Conditional Search function (see ROM Function Commands). The device also generates a time stamp of when the alarm occurred and begins recording the duration of the alarming temperature.
DS1921H/Z
and periods (12 periods for too hot and 12 for too cold). The date and time of each of these periods can be determined from the Mission Time Stamp and the time distance between each temperature reading.
ALARM TIME STAMPS AND DURATIONS ADDRESS MAP Figure 8
ADDRESS DESCRIPTION ALARM EVENT 0220h Mission Samples Counter Low Byte
0221h Mission Samples Counter Center Byte Low Alarm 1
0222h Mission Samples Counter High Byte
0223h Alarm Duration Counter
0224h to 0227h Alarm Time Stamp and Duration Low Alarm 2
0228h to 024Fh Alarm Time Stamp and Durations Low Alarms 3 to 12
0250h Mission Samples Counter Low Byte
0251h Mission Samples Counter Center Byte High Alarm 1
0252h Mission Samples Counter High Byte
0253h Alarm Duration Counter
0254h to 0257h Alarm Time Stamp and Duration High Alarm 2
0258h to 027Fh Alarm Time Stamp and Durations High Alarms 3 to 12 The alarm time stamp is a copy of the Mission Samples Counter when the alarm first occurred. The least significant byte is stored at the lower address. One address higher than the time stamp the DS1921H/Z maintains a 1-byte duration counter that stores the number of samples the temperature was found to be beyond the threshold. If this counter has reached its limit after 255 consecutive temperature readings and the temperature has not yet returned to within the tolerance band, the device will issue another time stamp at the next higher alarm location and open another counter to record the duration. If the temperature returns to normal before the counter has reached its limit, the duration counter of the particular time stamp will not increment any further. Should the temperature again cross this threshold, it will be recorded at the next available alarm location. This algorithm is implemented for the low as well as for the high temperature threshold.
MISSIONING The typical task of the DS1921H/Z is recording the temperature of a temperature-sensitive object. Before the device can perform this function, it needs to be configured. 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. The clock must be running (EOSC = 0) for at least one second. Setting a RTC alarm is optional. The memory assigned to storing alarm time stamps and durations, temperature histogram, as well as the Mission Time Stamp, Mission Samples Counter, Mission Start Delay, and Sample Rate must be cleared using the Memory Clear command. In case there were temperature alarms in the previous mission, the TLF and THF flags need to be cleared manually. To enable the device for a mission, the EM flag must be set to 0. These are general settings that have to be made regardless of the type of object to be monitored and the duration of the mission. Next, the low temperature and high temperature thresholds to specify the temperature tolerance band
DS1921H/Z The state of the Search Condition bits in the Control Register does not affect the mission. If multiple devices are connected to form a 1-Wire net, the setting of the search condition will enable devices to participate in the conditional search if certain events such as timer or temperature alarm have occurred. Details on the search conditions are found in the section ROM Function Commands later in this document and in the Control Register description. 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 recent temperature history 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 2048 to calculate the value of the sample rate (number of minutes between temperature conversions). If the estimated duration of a mission is 10 days (= 14400 minutes) for example, then the 2048-byte capacity of the datalog memory would be sufficient to store a new value every 7 minutes. If the datalog memory of the DS1921H/Z is not large enough to store all temperature readings, one can use several devices and set the Mission Start Delay to values that make the second device start recording 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 recorded temperature log. After the RO bit and the Mission Start Delay are set, the Sample Rate Register is the last element of data that is written. 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. This increments both the Mission Samples Counter and Device Samples Counter. All subsequent temperature measurements are taken on minute boundaries specified by the value in the Sample Rate Register. One may read the memory of the DS1921H/Z to watch the mission as it progresses. Care should be taken to avoid memory access conflicts. See section Memory Access Conflicts for details.
MEMORY/CONTROL FUNCTION COMMANDS The Memory/Control Function Flow Chart (Figure 10) describes the protocols necessary for accessing the memory and the special function registers of the DS1921H/Z. An example on how to use these and other functions to set up the DS1921H/Z for a mission is included at the end of this document, preceding the Electrical Characteristics section. The communication between master and DS1921H/Z takes place either at regular speed (default, OD = 0) or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive mode, the DS1921H/Z assumes regular speed. Internal memory access during a mission has priority over external access through the 1-Wire interface. This can affect the Read Memory commands described below. See section Memory Access Conflicts for details.
ADDRESS REGISTERS AND TRANSFER STATUS Because of the serial data transfer, the DS1921H/Z 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 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. Bit 5 of the E/S
DS1921H/Z
byte offset. If the target address for a Write command is 13Ch, for example, then the scratchpad will store incoming data beginning at the byte offset 1Ch and will be full after only 4 bytes. The corresponding ending offset in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point to the beginning of a new page, (i.e., the byte offset will be 0). Thus, the full 32-byte capacity of the scratchpad is available, resulting also in the ending offset of 1Fh. However, it is possible to write 1 or several contiguous bytes somewhere within a page. The ending offset together with the Partial and Overflow Flag is mainly a means to support the master checking the data integrity after a Write command. The highest valued bit of the E/S Register, called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been received and executed. Writing data to the scratchpad clears this flag.
ADDRESS REGISTERS Figure 9 Bit # 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
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. As preamble to the scratchpad data, the DS1921H/Z sends the requested target address TA1 and TA2 and the contents of the E/S Register. If the PF flag is set, data did not arrive correctly in the scratchpad. The master does not need to continue reading; it can start a new trial to write data to the scratchpad. Similarly, a set AA flag indicates that the 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. Now the master can continue verifying every data bit. After the master has verified the data, it has to send the Copy Scratchpad command. This command must be followed exactly by the data of the three address registers TA1, TA2 and E/S as the master has read them verifying the scratchpad. As soon as the DS1921H/Z has received these bytes, it will copy the data to the requested location beginning at the target address.
Write Scratchpad Command [0Fh] After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by the data to be written to the scratchpad. The data will be written to the scratchpad starting at the byte offset (T4:T0). The ending offset (E4:E0) will be the byte offset at which the master stops writ-ing data. Only full data bytes are accepted. If the last data byte is incomplete, its content will be ignored and the partial byte flag (PF) will be set.
DS1921H/Z
byte sent by the master. This CRC is generated using the CRC16 polynomial by first 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. The master may end the Write Scratchpad command at any time. However, if the ending offset is 11111b, the master may send 16 read time slots and will receive an inverted CRC16 generated by the DS1921H/Z.
The range 200h to 213h of the register page is protected during a mission. See Figure 6, Register Page Map, for the access type of the individual registers between and during missions.
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 9. Regardless of the actual ending offset, the master may read 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 DS1921H/Z until a reset pulse is issued.
Copy Scratchpad [55h] This command is used to copy data from the scratchpad to the writable memory sections. Applying Copy Scratchpad to the Sample Rate Register can start a mission provided that several preconditions are met. See Mission Start and Logging Process description and the flow chart in Figure 11 for details. 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). If the pattern matches, the AA (Authorization Accepted) flag will be set and the copy will begin. A pattern of alternating 1s and 0s will be 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 will be ignored. Copy typically takes 2µs per byte. The data to be copied is determined by the three address registers. The scratchpad data from the begin-ning offset through the ending offset will be copied, starting at the target address. Anywhere from 1 to 32 bytes may be copied to memory with this command. The AA flag will remain at logic 1 until it is cleared by the next Write Scratchpad command. Note that Copy Scratchpad when applied to the address range 200h to 213h during a mission will end the mission.
Read Memory [F0h] The Read Memory command may be used to read the entire memory. After issuing the command, the master must provide the 2-byte target address. After the 2 bytes, the master reads data beginning from the target address and may continue until the end of memory, at which point logic 0s will be read. It is im-portant to realize that the target address registers will contain the address provided. 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, it is recommended to packetize data into data packets of the size of one memory page each. Such a packet would typically store a 16-bit CRC with each page of data to ensure rapid, error-free data transfers that eliminate having to read a page multiple times to verify whether if the received data is cor-
DS1921H/Z
MEMORY/CONTROL FUNCTION FLOW CHART Figure 10-1 Master TX Memory orControl Fkt. Command
0FHWriteScratchpad
DS1921 sets Scratch-pad Offset = (T4:T0)and Clears (PF, AA)
Master TX Data Byteto Scratchpad Offset
DS1921 sets (E4:E0)= Scratchpad Offset
MasterTX Reset
Scratch-pad Offset =11111b
Master RX CRC16 ofCommand, Address, Data
DS1921 Incre-ments Scratch-pad Offset
Master RX "1"s
MasterTX Reset
MasterTX Reset
PartialByte Written
PF = 1
AAHReadScratchpad
Master RX EndingOffset with DataStatus (E/S)
MasterTX Reset
Scratch-pad Offset =11111b
Master RX CRC16 ofCommand, Address Data,E/S Byte, and Data Startingat the Target Address
DS1921 Incre-ments Scratch-pad Offset
Master RX "1"s
MasterTX Reset
DS1921 sets Scratch-pad Offset = (T4:T0)
Master RX Data Bytefrom Scratchpad Offset
From ROM FunctionsFlow Chart (Figure 12)
To ROM FunctionsFlow Chart (Figure 12)
DS1921 setsEMCLR = 0
Master TXTA1 (T7:T0), TA2 (T15:T8)
DS1921 setsEMCLR = 0
Master RXTA1 (T7:T0), TA2 (T15:T8)
To Figure 102nd Part
From Figure 102nd Part
DS1921H/Z
MEMORY/CONTROL FUNCTION FLOW CHART Figure 10-2 To Figure 103rd Part55HCopyScratchpad
Master TXE/S Byte
AuthorizationCode Match
DS1921 Copies ScratchpadData to Memory
CopyingFinished
MasterTX Reset
MasterTX Reset
AA = 1
F0HReadMemory
MasterTX Reset
End ofMemory
Master RX "0"s
DS1921 sets MemoryAddress = (T15:T0)
Master RX Data Bytefrom Memory Address
Master TXTA1 (T7:T0), TA2 (T15:T8)
MasterRX "1"s
DS1921 TX "0"
DS1921 TX "1"
MasterTX Reset
MasterRX "1"s
Master TXTA1 (T7:T0), TA2 (T15:T8)
DS1921 Incre-ments AddressCounter
DS1921 setsEMCLR = 0DS1921 setsEMCLR = 0
From Figure 101st Part
To Figure 101st PartFrom Figure 103rd Part
DS1921H/Z
MEMORY/CONTROL FUNCTION FLOW CHART Figure 10-3 A5HRead Mem.w/CRC
DS1921 sets MemoryAddress = (T15:T0)
Master RX Data Bytefrom Memory Address
End ofMemory
MasterTX Reset
CRC OK
DS1921 Incre-ments AddressCounter
End of Page
Master RX CRC16 ofCommand, Address, Data(1st Pass); CRC16 of Data(Subsequent Passes)
Master TXReset
Decision madeby DS1921
Decision madeby Master
Master TXTA1 (T7:T0), TA2 (T15:T8)
DS1921 setsEMCLR = 0
From Figure 102nd Part
To Figure 102nd Part
To Figure 104th Part
From Figure 104th Part
Master RX00 Byte
DS1921H/Z
MEMORY/CONTROL FUNCTION FLOW CHART Figure 10-4 3CHClearMemory
EMCLR = 1
DS1921 clears MissionTime Stamp, MissionSamples Counter,Mission Start Delay,Sample Rate Register
DS1921 setsEMCLR = 0
44HConvertTemp.
MasterTX Reset
DS1921 StartsTemperatureConversion Process
MasterTX Reset
Mission inProgress
DS1921 setsMEMCLR = 1
DS1921 clearsHistogram Memory
DS1921 clears Alarm TimeStamps and Durations
DS1921 setsEMCLR = 0
MasterTX Reset
From Figure 103rd Part
To Figure 103rd Part
DS1921 setsTCB\ = 0
DS1921 Performs aTemp. Conversion
DS1921 copies Resultto Address 0211h
DS1921 setsTCB\ = 1
Temperature Con-version Process
End of Process
DS1921H/Z
Read Memory with CRC [A5h] The Read Memory with CRC command is used to read memory data that cannot be packetized, such as the register page and the data recorded by the device during a mission. 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. After having sent the command code of the Read Memory with CRC command, the bus master sends a 2-byte address (TA1 = T7:T0, TA2 = T15:T8) that indicates a starting byte location. With the subsequent read data time slots the master receives data from the DS1921H/Z starting at the initial address and continuing until the end of a 32-byte page is reached. At that point the bus master will send 16 additional read data time slots and receive an inverted 16-bit CRC. With subsequent read data time slots the master will receive data starting at the beginning of the next page followed again by the inverted CRC for that page. This sequence will continue until the bus master resets the device. 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 two 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 will receive logical 0s from the DS1921H/Z and inverted CRC16s at page boundaries until a reset pulse is issued. The Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
Clear Memory [3Ch] The Clear Memory command is used to clear the Sample Rate, Mission Start Delay, Mission Time Stamp, and Mission Samples Counter in the register page and the Temperature Alarm Memory and the Temperature Histogram Memory. These memory areas must be cleared for the device to be set up for another mission. The Clear Memory command does not clear the datalog memory or the temperature and timer alarm flags in the Status Register. The RTC oscillator must be on and have counted at least 1 second, before issuing the command. For the Clear Memory command to function the EMCLR bit in Control Register must be set to 1, and the Clear Memory command must be issued with the very next access to the device’s memory functions. Issuing any other memory function command will reset the EMCLR bit. The Clear Memory process takes 500µs. When the command is completed the MEMCLR bit in the Status Register will read 1 and the EMCLR bit will be 0.
Convert Temperature [44h] If a mission is not in progress (MIP = 0) the Convert Temperature command can be issued to measure the current temperature of the device. The result of the temperature conversion will be found at memory address 211h in the register page. This command takes maximum 360ms to complete. During this time the device remains fully accessible for memory/control and ROM function commands.
DS1921H/Z
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 (EM = 0). If the new sample rate is different from zero, the value will be copied to the sample rate register. At the same time the MIP bit will be set and the MEMCLR bit will be cleared to indicate that the device is on a mission. Next the Mission Start Delay counter will start decrementing every minute until it is down to 0. Now the DS1921H/Z will wait until the next minute boundary and start the logging process, which as its first action copies the applicable RTC registers to the Mission Time Stamp.
MISSION START AND LOGGING PROCESS Figure 11 The Mission Start Process is invoked when the Copy Scratchpad function is used to set a new sample rateby writing to the Sample Rate Register at address 020Dh. One minute after the start delay countdown isover, the Logging Process begins and the Mission Start Process ends.
Logging Process
DS1921 sets DatalogAddress = 1000h
DS1921 MeasuresTemperature
DS1921 Updates His-togram, Device Sam-ples Counter, MissionSamples Counter andAlarm, if applicable
RO = 1
DS1921 Stores Temp.at Datalog Address
DS1921 Incrementslower 11 bits ofDatalog Address
DS1921 Stores Temp.at Datalog Address
DS1921 IncrementsDatalog Address
DatalogAddress =1800h
DS1921 WaitsOne SamplePeriodMIP = 1
End of Process
DS1921 Copies newSample Rate fromScratchpad to SampleRate Register
DS1921 sets MIP = 1;MEMCLR = 0
MIP = 1
MEMCLR = 1
EM = 0
New SampleRate = 0
Start DelayCounter = 0
Mission Start Process
DS1921 DecrementsStart Delay Counter
DS1921 Waits UntilNext Minute Boundary
DS1921 Copies RTC toMission Time Stamp
End of Process
DS1921 Sets MIP = 0MIP = 1DS1921LoggingProcess
DS1921 WaitsUntil NextMinuteBoundary
