DS1922L/DS1922T

General Description
The iButton® temperature loggers (DS1922L/DS1922T)
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. A total of
8192 8-bit readings or 4096 16-bit readings, taken at
equidistant intervals ranging from 1s to 273hr, can be
stored. Additionally, 512 bytes of SRAM store applicationspecific information and 64 bytes store calibration data. A
mission to collect data can be programmed to begin
immediately, after a user-defined delay, or after a temperature alarm. Access to the memory and control functions
can be password protected. The DS1922L/DS1922T are
configured and communicate with a host-computing
device through the serial 1-Wire® protocol, which requires
only a single data lead and a ground return. EachDS1922L/DS1922T is factory lasered with a guaranteed
unique 64-bit registration number that allows for absolute
traceability. The durable stainless-steel package is highly
resistant to environmental hazards such as dirt, moisture,and shock. Accessories permit the DS1922L/DS1922T to
be mounted on almost any object, including containers,
pallets, and bags.

Applications
High-Temperature Logging (Process Monitoring,
Industrial Temperature Monitoring)Temperature Logging in Cold Chain, Food Safety, Bio
Science, and Pharmaceutical and Medical Products

Benefits and Features• High Accuracy, Full-Featured Digital Temperature
Logger Simplifies Temperature Data Collection and
Dissemination of Electronic Temperature Record• Temperature Accuracy of ±0.5°C from -10°C to+65°C (DS1922L), ±0.5°C from +20°C to +75°C(DS1922T), with Software Corrections• Measures Temperature with 8-Bit (0.5°C) or 11-Bit(0.0625°C) Resolution• Operating Temperature Range: DS1922L: -40°C to+85°C; DS1922T: 0°C to +125°C• Automatically Wakes Up, Measures Temperature,and Stores Values in 8kB of Data-Log Memory in
8- or 16-Bit Format• Sampling Rate from 1s Up to 273hr• Programmable High and Low Trip Points for
Temperature Alarms• Programmable Recording Start Delay After Elapsed
Time or Upon a Temperature Alarm Trip Point

19-4990; Rev 13; 3/15

iButton Temperature Loggers
with 8KB Datalog Memory• 512 Bytes of General-Purpose Memory Plus

64 Bytes of Calibration Memory• Two-Level Password Protection of All Memory andConfiguration Registers• Individually Calibrated in a NIST-Traceable

Chamber• Complies to Standard EN12830• Rugged Construction Survives Harsh Environments• Water Resistant Enclosure (IP56) or Waterproof if

Placed Inside DS9107 iButton Capsule (Exceeds
Water Resistant 3 ATM Requirements)• CE, FCC, and UL913 Certifications• Simple Serial Port Interfaces to Most Microcontrollers
for Rapid Data Transfer• Communicates to Host with a Single Digital Signal
Up to 15.4kbps at Standard Speed or Up to
125kbps in Overdrive Mode Using 1-Wire Protocol• Quick Access to Alarmed Devices Through 1-Wire
Conditional Search Function

Ordering InformationPART

TEMP RANGE

DS1922L-F5#-40°C to +85°C

PIN-PACKAGE
F5 CanDS1922T-F5#

0°C to +125°C

F5 Can#Denotes a RoHS-compliant device that may include lead(Pb)that is exempt under the RoHS requirements.

Examples of Accessories
PART
DS9096P

ACCESSORY
Self-Stick Adhesive Pad

DS9101

Multipurpose Clip

DS9093RA

Mounting Lock Ring

DS9093A

Snap-in FOB

DS9092iButton Probe

Common iButton Device Features and Pin Configuration
appear at end of data sheet.

iButton and 1-Wire are registered trademarks of Maxim
Integrated Products, Inc.

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Absolute Maximum Ratings
IO Voltage Range to GND ........................................-0.3V to +6V
IO Sink Current....................................................................20mA
Operating Temperature Range
DS1922L ...........................................................-40°C to +85°C
DS1922T ............................................................0°C to +125°C

Junction Temperature ......................................................+150°C
Storage Temperature Range*
DS1922L..........................................................-40°C to +85°C*
DS1922T ...........................................................0°C to +125°C**Storage or operation above +50°C significantly reduces battery life.
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Electrical Characteristics(VPUP = +3.0V to +5.25V.)
PARAMETER
Operating Temperature

SYMBOLTACONDITIONS

MIN

TYP

MAX

DS1922L (Note 1)

-40

+85

DS1922T (Note 1)

0

+125

UNITS
°C

IO PIN: GENERAL DATA
1-Wire Pullup Resistance

RPUP(Notes 2, 3)

Input Capacitance

CIO(Note 4)

100

800

pF

Input Load CurrentIL

IO pin at VPUP

6

10

μA

High-to-Low Switching Threshold

VTL(Notes 5, 6)

3.2

VInput Low Voltage

VIL(Notes 2, 7)

Low-to-High Switching Threshold

VTH(Notes 5, 8)

Switching Hysteresis

VHY(Note 9)Output Low Voltage

VOL

At 4mA (Note 10)

Recovery Time (Note 2)

Rising-Edge Hold-Off TimeTime-Slot Duration (Note 2)

tREC

tREH
tSLOT

2.2

0.4

k

0.3

V

0.7

3.4

V

0.09

N/A

V

0.4

V

Standard speed, RPUP = 2.2k

5Overdrive speed, RPUP = 2.2k

2Overdrive speed, directly prior to reset
pulse; RPUP = 2.2k

5(Note 11)

0.6

Standard speed

65

Overdrive speed, VPUP > 4.5V

8

Overdrive speed (Note 12)

9.5

μs

2.0

μs
μs

IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE

Reset Low Time (Note 2)

Presence-Detect High Time

Presence-Detect Fall Time
(Note 13)www.maximintegrated.com

tRSTL

tPDH

tFPD

Standard speed, VPUP > 4.5V

480

720

Standard speed (Note 12)

690

720

Overdrive speed, VPUP > 4.5V

48

80

Overdrive speed (Note 12)7080Standard speed, VPUP > 4.5V

15

60

Standard speed (Note 12)

15

63.5

Overdrive speed (Note 12)27Standard speed, VPUP > 4.5V

1.55Standard speed

1.5

8Overdrive speed

0.15

1

μs

μs

μs

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Electrical Characteristics (continued)(VPUP = +3.0V to +5.25V.)
PARAMETER

Presence-Detect Low Time

Presence-Detect Sample Time
(Note 2)SYMBOLtPDL

tMSP

CONDITIONS

MIN

TYP

MAX

Standard speed, VPUP > 4.5V

60

240

Standard speed (Note 12)

60

287

Overdrive speed, VPUP > 4.5V (Note 12)724

Overdrive speed (Note 12)728Standard speed, VPUP > 4.5V

65

75

Standard speed

71.5

75

Overdrive speed

89Standard speed

60

120

Overdrive Speed, VPUP > 4.5V (Note 12)612Overdrive speed (Note 12)

7.5

12

UNITS

μs

μs

IO PIN: 1-Wire WRITE
Write-Zero Low Time
(Notes 2, 14)
Write-One Low Time
(Notes 2, 14)

tW0L

tW1L

Standard speed

515

Overdrive speed

1

1.95

μs

μs

IO PIN: 1-Wire READ
Read Low Time
(Notes 2, 15)tRL

Read Sample Time
(Notes 2, 15)tMSR

Standard speed

515 - 

Overdrive speed

11.95 - Standard speedtRL + 15

Overdrive speedtRL + 

1.95

μs
μs

REAL-TIME CLOCK
See RTC Accuracy
graphs

AccuracyFrequency Deviation

F-40°C to +85°C

-300

+60

0°C to +125°C

-600

+60

min/
month
PPM

TEMPERATURE CONVERTER
8-bit mode

30

75

16-bit mode (11 bits)

240

600

Conversion Time
(Note 16)tCONV

Thermal Response Time
Constant (Note 17)

RESP

Can package

130s

Conversion Error Without
Software Correction(Notes 18, 19)

See Temperature
Accuracy graphs°C

Conversion Error with Software
Correction(Notes 19, 20)

See Temperature
Accuracy graphs°C

Note 1:
Note 2:
Note 3:Note 4:Note 5:Note 6:ms

Guaranteed by design, not production tested to -40°C or +125°C.
System requirement.
Maximum allowable pullup resistance is a function of the number of 1-Wire devices in the system and 1-Wire recovery
times. The specified value here applies to systems with only one device and with the minimum 1-Wire recovery times. For
more heavily loaded systems, an active pullup such as that found in the DS2480B may be required.
Capacitance on the data pin could be 800pF when VPUP is first applied. If a 2.2kΩ resistor is used to pull up the data line,
2.5µs after VPUP has been applied, the parasite capacitance does not affect normal communications.
VTL and VTH are functions of the internal supply voltage, which is a function of VPUP and the 1-Wire recovery times. The
VTH and VTL maximum specifications are valid at VPUP = 5.25V. In any case, VTL < VTH < VPUP.
Voltage below which, during a falling edge on IO, a logic 0 is detected.

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iButton Temperature Loggers
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DS1922L/DS1922T

Electrical Characteristics (continued)(VPUP = +3.0V to +5.25V.)
Note 7: The voltage on IO must be less than or equal to VILMAX whenever the master drives the line low.
Note 8: Voltage above which, during a rising edge on IO, a logic 1 is detected.
Note 9: After VTH is crossed during a rising edge on IO, the voltage on IO must drop by VHY to be detected as logic 0.
Note 10: The I-V characteristic is linear for voltages less than 1V.
Note 11: The earliest recognition of a negative edge is possible at tREH after VTH has been previously reached.
Note 12: Numbers in bold are not in compliance with the published iButton device standards. See the Comparison Table.
Note 13: Interval during the negative edge on IO at the beginning of a presence-detect pulse between the time at which the voltage
is 90% of VPUP and the time at which the voltage is 10% of VPUP.
Note 14: ε in Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to VTH. The actual
maximum duration for the master to pull the line low is tW1LMAX + tF - ε and tW0LMAX + tF - ε, respectively.
Note 15: δ in Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input-highthreshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF.
Note 16: To conserve battery power, use 8-bit temperature logging whenever possible.
Note 17: This number was derived from a test conducted by Cemagref in Antony, France, in July 2000:
www.cemagref.fr/English/index.htm Test Report No. E42.
Note 18: Includes +0.1/-0.2°C calibration chamber measurement uncertainty.
Note 19: Warning: Maxim data-logger products are 100% tested and calibrated at time of manufacture to ensure that they meet alldata sheet parameters, including temperature accuracy. As with any sensor-based product, user shall be responsible foroccasionally rechecking the temperature accuracy of the product to ensure it is still operating properly. Furthermore, aswith all products of this type, when deployed in the field and subjected to handling, harsh environments, or other hazards/
use conditions, there may be some extremely small but nonzero logger failure rate. In applications where the failure of any
logger is a concern, user shall assure that redundant (or other primary) methods of testing and determining the handling
methods, quality, and fitness of the articles and products are implemented to further mitigate any risk.
Note 20: Assumes using calibration memory with calibration equations for error compensation. Includes +0.1/-0.2°C calibrationchamber measurement uncertainty. Guaranteed by design.

Comparison Table
LEGACY VALUESSTANDARD SPEED(μs)

PARAMETERDS1922L/DS1922T VALUESOVERDRIVE SPEED(μs)

STANDARD SPEED(μs)

OVERDRIVE SPEED
(μs)

MIN

MAX

MIN

MAX

MIN

MAX

MIN

MAX

t SLOT (including tREC)

61(undefined)

7(undefined)

65 *(undefined)

9.5(undefined)

tRSTL

480

(undefined)

48

80

690

720

70

80

t PDH

15

60

2

6

15

63.5

2

7

t PDL

60

240

8

24

60

287

7

28

tW0L

60

120

6

16

60

120

7.5

12

*Intentional change; longer recovery time requirement due to modified 1-Wire front-end.
Note: Numbers in bold are not in compliance with the published iButton device standards.

iButton Can Physical Specification
SIZE

See the Package Information section.

WEIGHT

Ca. 3.3 grams

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922L Minimum Product Lifetime vs. Temperature, Slow Sampling
EVERY MINUTENO SAMPLESEVERY 10 MINUTESEVERY 60 MINUTESEVERY 3 MINUTESOSCILLATOR OFF

10

8-BIT MINIMUM PRODUCT LIFETIME (YEARS)

9
8
7
6
5
4
3
2
1
0
-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

EVERY MINUTENO SAMPLESEVERY 10 MINUTESEVERY 60 MINUTESEVERY 3 MINUTESOSCILLATOR OFF

EVERY 30 MINUTESEVERY 300 MINUTES

11-BIT MINIMUM PRODUCT LIFETIME (YEARS)

10
9
8
7
6
5
4
3
2
1
0
-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922L Minimum Product Lifetime vs. Temperature, Fast Sampling
EVERY SECOND
EVERY 30 SECONDSEVERY 10 SECONDSEVERY 3 SECONDSEVERY 60 SECONDS

8-BIT MINIMUM PRODUCT LIFETIME (DAYS)

350
300
250
200
150
100
50
0
-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

70

80

TEMPERATURE (°C)

EVERY SECOND
EVERY 30 SECONDSEVERY 10 SECONDSEVERY 3 SECONDSEVERY 60 SECONDS

11-BIT MINIMUM PRODUCT LIFETIME (DAYS)

100

80

60

40

20

0
-40

-30

-20

-10

0

10

20

30

40

50

60

TEMPERATURE (°C)

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922T Minimum Product Lifetime vs. Temperature, Slow Sampling
EVERY MINUTE
EVERY 60 MINUTESEVERY 10 MINUTESOSCILLATOR OFF

EVERY 3 MINUTESNO SAMPLES

108-BIT MINIMUM PRODUCT LIFETIME (YEARS)

9
8
7
6
5
4
3
2
1
0
0

10

20

30

40

50

60

70

80

90

100

110

120

TEMPERATURE (°C)

EVERY MINUTE
EVERY 60 MINUTESEVERY 10 MINUTESOSCILLATOR OFF

EVERY 3 MINUTESNO SAMPLESEVERY 30 MINUTESEVERY 300 MINUTES

11-BIT MINIMUM PRODUCT LIFETIME (YEARS)

10
9
8
7
6
5
4
3
2
1
0
0

10

20

30

40

50

60

70

80

90

100

110

120

TEMPERATURE (°C)

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922T Minimum Product Lifetime vs. Temperature, Fast Sampling

EVERY SECOND
EVERY 30 SECONDSEVERY 10 SECONDSEVERY 3 SECONDSEVERY 60 SECONDS

8-BIT MINIMUM PRODUCT LIFETIME (DAYS)

350
300
250
200
150
100
50
0
0

10

20

30

40

50

60

70

80

90

100

110

120

100

110

120

TEMPERATURE (°C)

EVERY SECOND
EVERY 30 SECONDSEVERY 10 SECONDSEVERY 3 SECONDSEVERY 60 SECONDS

11-BIT MINIMUM PRODUCT LIFETIME (DAYS)

100

80

60

40

20

0
0

10

20

30

40

50

60

70

80

90

TEMPERATURE (°C)

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922L Minimum Product Lifetime vs. Sample Rate

8-BIT MINIMUM PRODUCT LIFETIME (YEARS)

10

0°C
+40°C
-40°C
+60°C

+75°C
1
+85°C

0.1

0.01
0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

11-BIT MINIMUM PRODUCT LIFETIME (YEARS)

10

0°C
+40°C
-40°C
+60°C
+75°C

1

+85°C

0.1

0.01

0.001
0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922T Minimum Product Lifetime vs. Sample Rate

10

0°C
+40°C

8-BIT MINIMUM PRODUCT LIFETIME (YEARS)

+60°C
+75°C
1

+85°C
+95°C

+110°C
0.1+125°C

0.01
0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

11-BIT MINIMUM PRODUCT LIFETIME (YEARS)

10

0°C
+40°C
+60°C
+75°C

1

+85°C
+95°C
+110°C

0.1+125°C

0.01

0.001
0.01

0.1

1

10

100

MINUTES BETWEEN SAMPLES

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

DS1922L Temperature Accuracy
2.0

1.5

ERROR (°C)

1.0
UNCORRECTED MAXIMUM ERROR
0.5
SW CORRECTED MAXIMUM ERROR
0.0
SW CORRECTED MINIMUM ERROR-0.5
UNCORRECTED MINIMUM ERROR
-1.0
-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

90

100

110

120

TEMPERATURE (°C)
NOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.

DS1922T Temperature Accuracy
2.5
2.0
1.5

ERROR (°C)

1.0

UNCORRECTED MAXIMUM ERROR

0.5
SW CORRECTED MAXIMUM ERROR
0.0
SW CORRECTED MINIMUM ERROR-0.5

UNCORRECTED MINIMUM ERROR
-1.0
-1.5
-2.0
-2.5
0

10

20

30

40

50

60

70

80

TEMPERATURE (°C)
NOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.

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iButton Temperature Loggers
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DS1922L/DS1922T

DS1922L RTC Accuracy (Typical)
2.0

1.0

DRIFT (MINUTES/MONTH)

0.0

-1.0

-2.0

-3.0

-4.0

-5.0
-40

-30

-20

-10

0

10

20

30

40

50

60

70

80

80

90

100

110

120

TEMPERATURE (°C)

DS1922T RTC Accuracy (Typical)
2.0

0.0

DRIFT (MINUTES/MONTH)

-2.0

-4.0

-6.0

-8.0

-10.0

-12.0
0

10

20

30

40

50

60

70

TEMPERATURE (°C)

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DS1922L/DS1922T

iButton Temperature Loggers
with 8KB Datalog Memory

Detailed Description

and another one for a read/write password, can only be
written, never read.
Figure 2 shows the hierarchical structure of the 1-Wireprotocol. The bus master must first provide one of theeight ROM function commands: Read ROM, Match
ROM, Search ROM, Conditional Search ROM, Skip
ROM, Overdrive-Skip ROM, Overdrive-Match ROM, orResume. Upon completion of an Overdrive ROM command executed at standard speed, the device enters
overdrive mode, where all subsequent communication
occurs at a higher speed. The protocol required forthese ROM function commands is described in Figure
11. After a ROM function command is successfully executed, the memory and control functions become
accessible and the master can provide any one of theeight available commands. The protocol for these memory and control function commands is described in
Figure 9. All data is read and written least significant
bit first.

The DS1922L is an ideal device to monitor for extended
periods of time the temperature of any object it is
attached to or shipped with, such as fresh produce,
medical drugs and supplies, and for use in refrigeratorsand freezers. With its shifted temperature range, theDS1922T is suited to monitor processes that requiretemperatures close to the boiling point of water, such as
pasteurization of food items. Note that the initial sealinglevel of the DS1922L/DS1922T achieves the equivalentof IP56. Aging and use conditions can degrade theintegrity of the seal over time, so for applications withsignificant exposure to liquids, sprays, or other similar
environments, it is recommended to place theDS1922L/DS1922T in the DS9107 iButton capsule. The
DS9107 provides a watertight enclosure that has been
rated to IP68 (refer to Application Note 4126:
Understanding the IP (Ingress Protection) Ratings ofiButton Data Loggers and Capsules). Software for setup
and data retrieval through the 1-Wire interface is available for free download from the iButton device website(www.ibutton.com). This software also includes drivers
for the serial and USB port of a PC and routines toaccess the general-purpose memory for storing application-specific or equipment-specific data files.
All iButton data loggers are calibrated/validated against
NIST traceable reference devices. Maxim offers a web
application to generate validation certificates for theDS1922L, DS1922T, DS1922E, and DS1923 (temperature portion only) data loggers. Input is the device’s
ROM code (or list of codes) and the output is a validation certificate in PDF format. For more information,refer to Application Note 4629: iButton Data-Logger
Calibration and NIST Certificate FAQs.

Overview
The block diagram in Figure 1 shows the relationships
between the major control and memory sections of theDS1922L/DS1922T. The devices have six main data
components: 64-bit lasered ROM; 256-bit scratchpad;
512-byte general-purpose SRAM; two 256-bit register
pages of timekeeping, control, status, and counter registers, and passwords; 64 bytes of calibration memory;and 8192 bytes of data-logging memory. Except for the
ROM and the scratchpad, all other memory is arranged
in a single linear address space. The data-logging
memory, counter registers, and several other registers
are read only for the user. Both register pages are write
protected while the device is programmed for a mission. The password registers, one for a read password

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Parasite PowerThe block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever
the IO input is high. IO provides sufficient power aslong as the specified timing and voltage requirements
are met. The advantages of parasite power are twofold: 1) By parasiting off this input, battery power is notconsumed for 1-Wire ROM function commands, and2) if the battery is exhausted for any reason, the ROM
may still be read normally. The remaining circuitry of
the DS1922 is solely operated by battery energy.

64-Bit Lasered ROM
Each DS1922L/DS1922T contains a unique ROM codethat is 64 bits long. The first 8 bits are a 1-Wire family
code. The next 48 bits are a unique serial number. The
last 8 bits are a cyclic redundancy check (CRC) of thefirst 56 bits (see Figure 3 for details). The 1-Wire CRC isgenerated using a polynomial generator consisting of ashift register and XOR gates as shown in Figure 4. The
polynomial is X8 + X5 + X4 + 1. Additional information
about the 1-Wire CRC is available in Application Note
27: Understanding and Using Cyclic Redundancy
Checks with Maxim iButton Products.
The shift register bits are initialized to 0. Then, startingwith the least significant bit of the family code, one bit
at a time is shifted in. After the 8th bit of the family code
has been entered, the serial number is entered. Afterthe last bit of the serial number has been entered, theshift register contains the CRC value. Shifting in the 8bits of CRC returns the shift register to all 0s.

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iButton Temperature Loggers
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DS1922L/DS1922T

1-Wire PORTROM
FUNCTIONCONTROL

IO

64-BITLASEREDROMMEMORYFUNCTIONCONTROL

3V LITHIUM

PARASITE-POWEREDCIRCUITRY

256-BITSCRATCHPADDS1922L
DS1922T
GENERAL-PURPOSE
SRAM(512 BYTES)INTERNALTIMEKEEPING,CONTROL REGISTERS,AND COUNTERS

32.768kHz
OSCILLATOR

THERMALSENSE

REGISTER PAGES(64 BYTES)CALIBRATION MEMORY(64 BYTES)ADCCONTROL
LOGIC

DATA-LOG MEMORY
8KB

Figure 1. Block Diagram

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iButton Temperature Loggers
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DS1922L/DS1922T

1-Wire NET

BUS
MASTEROTHER DEVICES

DS1922L/DS1922T
COMMAND LEVEL:AVAILABLE COMMANDS:DATA FIELD AFFECTED:

1-Wire ROM
FUNCTION COMMANDSREAD ROM
MATCH ROM
SEARCH ROM
CONDITIONAL SEARCH ROM
SKIP ROMRESUMEOVERDRIVE-SKIP ROM
OVERDRIVE-MATCH ROM

64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG, ALARM FLAGS, SEARCH CONDITIONS
RC-FLAGRC-FLAGRC-FLAG, OD-FLAG
64-BIT ROM, RC-FLAG, OD-FLAG

WRITE SCRATCHPADREAD SCRATCHPADCOPY SCRATCHPAD WITH PW
READ MEMORY WITH PW AND CRC
CLEAR MEMORY WITH PW

256-BIT SCRATCHPAD, FLAGS
256-BIT SCRATCHPAD
512-BYTE DATA MEMORY, REGISTERS, FLAGS, PASSWORDSMEMORY, REGISTERS, PASSWORDSMISSION TIMESTAMP, MISSION SAMPLES COUNTER,
START DELAY, ALARM FLAGS, PASSWORDSMEMORY ADDRESSES 020Ch TO 020Dh
FLAGS, TIMESTAMP, MEMORY ADDRESSES
020Ch TO 020Dh (WHEN LOGGING)
FLAGSDS1922L/DS1922T-SPECIFICMEMORY/CONTROL FUNCTION
COMMANDSFORCED CONVERSIONSTART MISSION WITH PW
STOP MISSION WITH PW

Figure 2. Hierarchical Structure for 1-Wire Protocol

MSB

LSB
8-BIT
CRC CODE

MSB

8-BIT FAMILY CODE
(41h)

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
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Maxim Integrated | 15

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

MemoryFigure 5 shows the DS1922L/DS1922T memory map.
Pages 0 to 15 contain 512 bytes of general-purpose
SRAM. The various registers to set up and control thedevice fill pages 16 and 17, called register pages 1
and 2 (see Figure 6 for details). Pages 18 and 19 provide storage space for calibration data. They can alternatively be used as an extension of the generalpurpose memory. The data-log logging memory starts
at address 1000h (page 128) and extends over 256
pages. The memory pages 20 to 127 are reserved for
future extensions. The scratchpad is an additional pagethat acts as a buffer when writing to the SRAM memoryor the register pages. The data memory can be written
at any time. The calibration memory holds data from thedevice calibration that can be used to further improve
the accuracy of 11-bit temperature readings. See theSoftware Correction Algorithm for Temperature section
for details. The last byte of the calibration memory pagestores an 8-bit CRC of the preceding 31 bytes. Page 19
is an exact copy of the data in page 18. While calibration memory can be overwritten by the user, this is notrecommended. See the Security by Password section
for ways to protect the memory. The access type for theregister pages is register-specific and depends onwhether the device is programmed for a mission. Figure
6 shows the details. The data-log memory is read only
for the user. It is written solely under supervision of the
on-chip control logic. Due to the special behavior of thewrite access logic (write scratchpad, copy scratchpad),
it is recommended to only write full pages at a time.
This also applies to the register pages and the calibration memory. See the Address Registers and Transfer
Status section for details.

32-BYTE INTERMEDIATE STORAGE
SCRATCHPADADDRESS
0000h TO 001Fh

32-BYTE GENERAL-PURPOSE SRAM
(R/W)

PAGE 00020h TO 01FFh

GENERAL-PURPOSE SRAM (R/W)

PAGES 1 TO 150200h TO 021Fh

32-BYTE REGISTER PAGE 1

PAGE 160220h TO 023Fh

32-BYTE REGISTER PAGE 2

PAGE 170240h TO 025Fh

CALIBRATION MEMORY PAGE 1 (R/W)

PAGE 180260h TO 027Fh

CALIBRATION MEMORY PAGE 2 (R/W)

PAGE 190280h TO 0FFFh(RESERVED FOR FUTURE EXTENSIONS)PAGES 20 TO 127

1000h TO 2FFFh

DATA-LOG MEMORY (READ ONLY)PAGES 128 TO 383

Figure 5. Memory Map

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Maxim Integrated | 16

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

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

0203h

0

0

0204h

CENT

0

0205h

BIT 5

BIT 3

10 Hour

0

BIT 2

BIT 1

BIT 0

Single Date

10
MonthsR/W

R

Sample
Rate

R/W

R

Temperature
Alarms

R/W

R

—

R/W

R

LatestTemperature

R

R

—

R

R

Single Years
Low Byte

0High Byte

0208h

Low Threshold

0209hHigh Threshold

020Ah(No Function with the DS1922L/DS1922T)

020Bh(No Function with the DS1922L/DS1922T)

020Ch

ACCESS*

Single Months

10 Years
0

FUNCTION

RealTime Clock
Registers

Single Hours

10 Date

0206h
0207h

BIT 4

Low Byte

0

020Dh

0

0

0

0

High Byte

020Eh(No Function with the DS1922L/DS1922T)

020Fh(No Function with the DS1922L/DS1922T)

0210h

0

0

0

0

0

0

ETHA

ETLA

Temperature
Alarm
Enable

R/W

R

0211h

1

1

1

1

1

1

0

0

—

R/W

R

0212h

0

0

0

0

0

0

EHSS

EOSC

RTC Control

R/W

R

R/W

R

0213h

1

1

SUTA

RO

(X)

TLFS

0

ETL

MissionControl

0214h

BOR

1

1

1

0

0

THF

TLF

Alarm Status

R

R

0215h

1

1

0

WFTA

MEMCLR

0MIP

0GeneralStatus

R

R

Start
Delay
Counter

R/W

R

0216h

Low Byte

0217h

Center Byte

0218h

High Byte*The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a
mission is in progress.

Figure 6. Register Pages Map

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Maxim Integrated | 17

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

ADDRESS

BIT 7

0219h

0

10 Seconds

Single Seconds

021Ah

0

10 Minutes

Single Minutes

021Bh

0

12/24

20 Hour
AM/PM

021Ch

0

0

021Dh

CENT

0

021Eh

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

10 Hour

Single Hours

10 Date0

BIT 1Single Date

10
Months

BIT 0

FUNCTIONACCESS*

MissionTimestamp

R

R

Single Months

10 Years

Single Years

021Fh(No Function; Reads 00h)

—

R

R

0220h

Low Byte

0221h

Center Byte

R

R

0222h

High Byte

MissionSamples
Counter0223h

Low Byte

0224h

Center Byte

R

R

0225h

High Byte

DeviceSamples
Counter0226h

Configuration CodeFlavor

R

R

0227h

EPW

PW Control

R/W

R

0228h

First Byte

…

…

W

—

022Fh

Eighth Byte

Read
AccessPassword

0230h

First Byte

…

…

W

—

0237h

Eighth Byte

Full
AccessPassword(No Function; All These Bytes Read 00h)

—

R

R

0238h
…
023Fh

*The left entry in the ACCESS column is valid between missions. The right entry shows the applicable access type while a
mission is in progress.

Figure 6. Register Pages Map (continued)

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Maxim Integrated | 18

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Detailed Register Descriptions
Timekeeping and Calendar
The RTC and calendar information is accessed byreading/writing the appropriate bytes in the register
page, address 0200h to 0205h. For readings to bevalid, all RTC registers must be read sequentially starting at address 0200h. Some of the RTC bits are set to
0. These bits always read 0 regardless of how they are
written. The number representation of the RTC registers
is binary-coded decimal (BCD) format.
The DS1922L/DS1922T’s RTC can run in either 12hr or
24hr mode. Bit 6 of the Hours register (address 0202h)
is defined as the 12hr- or 24hr-mode select bit. Whenhigh, the 12hr mode is selected. In the 12hr mode, bit 5is the AM/PM bit with logic 1 being PM. In the 24hr
mode, bit 5 is the 20hr bit (20hr to 23hr). The CENT bit,
bit 7 of the Months register, can be written by the user.
This bit changes its state when the years counter transitions from 99 to 00.
The calendar logic is designed to automatically compensate for leap years. For every year value that iseither 00 or a multiple of 4, the device adds a 29th ofFebruary. This works correctly up to (but not including)the year 2100.

Sample Rate
The content of the Sample Rate register (addresses
0206h, 0207h) specifies the time elapse (in seconds if
EHSS = 1, or minutes if EHSS = 0) between two temperature-logging events. The sample rate can be any
value from 1 to 16,383, coded as an unsigned 14-bit
binary number. If EHSS = 1, the shortest time between
logging events is 1s and the longest (sample rate =3FFFh) is 4.55hr. If EHSS = 0, the shortest is 1min andthe longest time is 273.05hr (sample rate = 3FFFh). The
EHSS bit is located in the RTC Control register ataddress 0212h. It is important that the user sets the
EHSS bit accordingly while setting the Sample Rateregister. Writing a sample rate of 0000h results in asample rate = 0001h, causing the DS1922L/DS1922T
to log the temperature either every minute or every
second depending upon the state of the EHSS bit.

RTC Registers Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

0200h

0

10 Seconds

Single Seconds

0201h

0

10 Minutes

Single Minutes

0202h

0

12/24

0203h

0

0

0204h

CENT

0

0205h

20 Hour
AM/PM

10 Hour

Single Hours

10 Date0

BIT 0Single Date

10 Months

Single Months

10 Years

Single Years

Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.

Sample Rate Register Bitmap
ADDRESS

BIT 7

BIT 6

0

0

0206h
0207h

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

Sample Rate Low
Sample Rate High

Note: During a mission, there is only read access to these registers. Bit cells marked “0” always read 0 and cannot be written to 1.

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Maxim Integrated | 19

DS1922L/DS1922T

iButton Temperature Loggers
with 8KB Datalog Memory

Temperature Conversion

This equation is valid for converting temperature readings stored in the data-log memory as well as for dataread from the Latest Temperature Conversion Result
register. The “-41” applies to the DS1922L. For theDS1922T, use “-1” instead of “-41.”
To specify the temperature alarm thresholds, the previous equations are resolved to:

The DS1922L’s temperature range begins at -40°C andends at +85°C. The temperature range for the DS1922T
begins at 0 and ends at +125°C. Temperature values
are represented as an 8-bit or 16-bit unsigned binary
number with a resolution of 0.5°C in 8-bit mode and0.0625°C in 16-bit mode.
The higher temperature byte TRH is always valid. In
16-bit mode, only the three highest bits of the lower
byte TRL are valid. The five lower bits all read 0. TRL is
undefined if the device is in 8-bit temperature mode. An
out-of-range temperature reading is indicated as 00h or
0000h when too cold and FFh or FFE0h when too hot.
With TRH and TRL representing the decimal equivalentof a temperature reading, the temperature value is calculated as:

TALM = 2 x ϑ(°C) + 82
The “+82” applies to the DS1922L. For the DS1922T, use“+2.” Because the temperature alarm threshold is only
one byte, the resolution or temperature increment is limited to 0.5°C. The TALM value must be converted into
hexadecimal format before it can be written to one of theTemperature Alarm Threshold registers (Low Alarm
address 0208h; High Alarm address 0209h).
Independent of the conversion mode (8-bit or 16-bit),only the most significant byte of a temperature conversion is used to determine whether an alarm is generated.

ϑ(°C) = TRH/2 - 41 + TRL/512 (16-bit mode,
TLFS = 1, see address 0213h)
ϑ(°C) = TRH/2 - 41 (8-bit mode, TLFS = 0,
see address 0213h)

Latest Temperature Conversion Result Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

BYTE

020Ch

T2

T1

T0

0

0

0

0

0

TRL

020Dh

T10

T9

T8

T7

T6

T5

T4

T3

TRH

Table 1. Temperature Conversion Examples
MODE

TRH

(°C)

TRL

HEX

DECIMALHEX

DECIMAL

DS1922L

DS1922T

8-Bit

54h

84

—

—

1.0

41.0

8-Bit

17h

23

—

—

-29.5

10.5

16-Bit

54h

84

00h

0

1.000

41.00016-Bit

17h

23

60h

96

-29.312510.6875

Table 2. Temperature Alarm Threshold Examples
(°C)

TALM (DS1922T)

(°C)

TALM (DS1922L)

HEX

DECIMALHEX

DECIMAL

65.5

85h

133

25.5

85h

133

30.0

3Eh

62

-10.0

3Eh

62

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Maxim Integrated | 20

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Temperature Sensor Control Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0210h

0

0

0

0

0

0

ETHA

ETLA

Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be
written to 1.

RTC Control Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0212h

0

0

0

0

0

0

EHSS

EOSC

Note: During a mission, there is only read access to this register. Bits 2 to 7 have no function. They always read 0 and cannot be
written to 1.

Temperature Sensor Alarm

RTC Control

The DS1922L/DS1922T have two Temperature Alarm
Threshold registers (address 0208h, 0209h) to store
values that determine whether a critical temperature
has been reached. A temperature alarm is generated if
the device measures an alarming temperature and thealarm signaling is enabled. The bits ETLA and ETHA
that enable the temperature alarm are located in theTemperature Sensor Control register. The temperature
alarm flags TLF and THF are found in the Alarm Status
register at address 0214h.
Bit 1: Enable Temperature High Alarm (ETHA). Thisbit controls whether, during a mission, the temperaturehigh alarm flag (THF) can be set, if a temperature conversion results in a value equal to or higher than thevalue in the Temperature High Alarm Threshold register.
If ETHA is 1, temperature high alarms are enabled. If
ETHA is 0, temperature high alarms are not generated.
Bit 0: Enable Temperature Low Alarm (ETLA). Thisbit controls whether, during a mission, the temperature
low alarm flag (TLF) can be set, if a temperature conversion results in a value equal to or lower than thevalue in the Temperature Low Alarm Threshold register.
If ETLA is 1, temperature low alarms are enabled. If
ETLA is 0, temperature low alarms are not generated.

To minimize the power consumption of the DS1922L/
DS1922T, the RTC oscillator should be turned off whenthese devices are not in use. The oscillator on/off bit islocated in the RTC Control register. This register also
includes the EHSS bit, which determines whether the
sample rate is specified in seconds or minutes.
Bit 1: Enable High-Speed Sample (EHSS). This bit
controls the speed of the sample rate counter. When set
to logic 0, the sample rate is specified in minutes. Whenset to logic 1, the sample rate is specified in seconds.
Bit 0: Enable Oscillator (EOSC). This bit controls the
crystal oscillator of the RTC. When set to logic 1, theoscillator starts. When written to logic 0, the oscillator
stops and the device is in a low-power data-retention
mode. This bit must be 1 for normal operation. A
Forced Conversion or Start Mission command automatically starts the RTC by changing the EOSC bit tologic 1.

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Maxim Integrated | 21

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Mission Control Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0213h

1

1

SUTA

RO

(X)

TLFS

0

ETL

Note: During a mission, there is only read access to this register. Bits 6 and 7 have no function. They always read 1 and cannot be
written to 0. Bits 1 and 3 control functions that are not available with the DS1922L/DS1922T. Bit 1 must be set to 0. Under this condition the setting of bit 3 becomes a “don’t care.”

Mission Control
The DS1922L/DS1922T are set up for operation by writing appropriate data to the special function registers,
which are located in the two register pages. The settings in the Mission Control register determine which
format (8 or 16 bits) applies and whether old data can
be overwritten by new data once the data-log memory
is full. An additional control bit can be set to tell theDS1922L/DS1922T to wait with logging data until a temperature alarm is encountered.
Bit 5: Start Mission Upon Temperature Alarm(SUTA). This bit specifies whether a mission begins
immediately (includes delayed start) or if a temperature
alarm is required to start the mission. If this bit is 1, thedevice performs an 8-bit temperature conversion at the
selected sample rate and begins with data logging only
if an alarming temperature (high alarm or low alarm)
was found. The first logged temperature is when thealarm occurred. However, the mission sample counter
does not increment. This functionality is guaranteed bydesign and not production tested.

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Bit 4: Rollover Control (RO). This bit controls whether,during a mission, the data-log memory is overwrittenwith new data or whether data logging is stopped oncethe data-log memory is full. Setting this bit to 1 enables
the rollover and data logging continues at the beginning, overwriting previously collected data. If this bit is0, the logging and conversions stop once the data-log
memory is full. However, the RTC continues to run and
the MIP bit remains set until the Stop Mission commandis performed.
Bit 2: Temperature Logging Format Selection(TLFS). This bit specifies the format used to store temperature readings in the data-log memory. If this bit is0, the data is stored in 8-bit format. If this bit is 1, the16-bit format is used (higher resolution). With 16-bit format, the most significant byte is stored at the lower
address.
Bit 0: Enable Temperature Logging (ETL). To set up
the device for a temperature-logging mission, this bit
must be set to logic 1. The recorded temperature values start at address 1000h.

Maxim Integrated | 22

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Alarm Status Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0214h

BOR

1

1

1

0

0

THF

TLF

Note: There is only read access to this register. Bits 4 to 6 have no function. They always read 1. Bits 2 and 3 have no function with
the DS1922L/DS1922T. They always read 0. The alarm status bits are cleared simultaneously when the Clear Memory Function is
invoked. See the Memory and Control Function Commands section for details.

General Status Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0215h

1

1

0

WFTA

MEMCLR

0MIP

0

Note: There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.

Alarm Status

General Status

The fastest way to determine whether a programmed
temperature threshold was exceeded during a mission
is by reading the Alarm Status register. In a networked
environment that contains multiple DS1922L/
DS1922T devices, the devices that encountered an
alarm can quickly be identified by means of theConditional Search command (see the 1-Wire ROM
Function Commands section). The temperature alarm
only occurs if enabled (see the Temperature Sensor
Alarm section). The BOR alarm is always enabled.
Bit 7: Battery-On Reset Alarm (BOR). If this bit reads
1, the device has performed a power-on reset. This
indicates that the device has experienced a shock big
enough to interrupt the internal battery power supply.
The device can still appear functional, but it has lost its
factory calibration. Any data found in the data-log memory should be disregarded.

The information in the General Status register tells thehost computer whether a mission-related command
was executed successfully. Individual status bits indicate whether the DS1922L/DS1922T are performing a
mission, waiting for a temperature alarm to trigger the
logging of data, or whether the data from the latest mission has been cleared.
Bit 4: Waiting for Temperature Alarm (WFTA). If thisbit reads 1, the Mission Start Upon Temperature Alarmwas selected and the Start Mission command was successfully executed, but the device has not yet experienced the temperature alarm. This bit is cleared after atemperature alarm event, but is not affected by the
Clear Memory command. Once set, WFTA remains set
if a mission is stopped before a temperature alarm
occurs. To clear WFTA manually before starting a new
mission, set the high temperature alarm (address
0209h) to -40°C and perform a forced conversion.
Bit 3: Memory Cleared (MEMCLR). If this bit reads 1,
the Mission Timestamp, Mission Samples Counter, andall the alarm flags of the Alarm Status register havebeen cleared in preparation of a new mission.
Executing the Clear Memory command clears thesememory sections. The MEMCLR bit returns to 0 as soon
as a new mission is started by using the Start Missioncommand. The memory must be cleared for a mission
to start.

Bit 1: Temperature High Alarm Flag (THF). If this bit
reads 1, there was at least one temperature conversion
during a mission revealing a temperature equal to or
higher than the value in the Temperature High Alarm
register. A forced conversion can affect the THF bit.
This bit can also be set with the initial alarm in the SUTA
= 1 mode.
Bit 0: Temperature Low Alarm Flag (TLF). If this bit
reads 1, there was at least one temperature conversion
during a mission revealing a temperature equal to or
lower than the value in the Temperature Low Alarm register. A forced conversion can affect the TLF bit. This bit
can also be set with the initial alarm in the SUTA = 1
mode.

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Bit 1: Mission in Progress (MIP). If this bit reads 1, thedevice has been set up for a mission and this mission isstill in progress. The MIP bit returns from logic 1 to logic
0 when a mission is ended. See the Start Mission with
Password and Stop Mission with Password sections.

Maxim Integrated | 23

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Mission Start Delay Counter Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

0216h

Delay Low Byte

0217h

Delay Center Byte

0218h

Delay High Byte

BIT 2

BIT 1

BIT 0

BIT 2

BIT 1

BIT 0

Note: During a mission, there is only read access to this register.

Mission Timestamp Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

0219h

0

10 Seconds

Single Seconds

021Ah

0

10 Minutes

Single Minutes

021Bh

0

12/24

021Ch

0

0

021Dh

CENT

0

021Eh

20 Hours
AM/PM

10 Hours

Single Hours

10 Date0Single Date

10 Months

Single Months

10 Years

Single Years

Note: There is only read access to this register.

Mission Samples Counter Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

0220h

Low Byte

0221h

Center Byte

0222hHigh Byte

BIT 2

BIT 1

BIT 0

Note: There is only read access to this register.

Mission Start Delay

Mission Timestamp

The content of the Mission Start Delay Counter registertells how many minutes must expire from the time a
mission was started until the first measurement of themission takes place (SUTA = 0) or until the device
starts testing the temperature for a temperature alarm(SUTA = 1). The Mission Start Delay is stored as an
unsigned 24-bit integer number. The maximum delay is
16,777,215min, equivalent to 11,650 days or roughly 31
years. If the start delay is nonzero and the SUTA bit is
set to 1, first the delay must expire before the device
starts testing for temperature alarms to begin logging
data.
For a typical mission, the Mission Start Delay is 0. If a
mission is too long for a single DS1922L/DS1922T tostore all readings at the selected sample rate, one canuse several devices and set the Mission Start Delay forthe second device to start recording as soon as thememory of the first device is full, and so on. The RO bit
in the Mission Control register (address 0213h) must be
set to 0 to prevent overwriting of collected data oncethe data-log memory is full.

The Mission Timestamp register indicates the date andtime of the first temperature sample of the mission.
There is only read access to the Mission Timestamp
register.

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Mission Progress Indicator
Depending on settings in the Mission Control register(address 0213h), the DS1922L/DS1922T log temperature in 8-bit or 16-bit format. The Mission Samples
Counter together with the starting address and the logging format (8 or 16 bits) provide the information to identify valid blocks of data that have been gathered during
the current (MIP = 1) or latest mission (MIP = 0). See theData-Log Memory Usage section for an illustration.
The number read from the Mission Samples Counter
indicates how often the DS1922L/DS1922T woke up
during a mission to measure temperature. The number
format is 24-bit unsigned integer. The Mission Samples
Counter is reset through the Clear Memory command.

Maxim Integrated | 24

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Device Samples Counter Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

0223h

Low Byte

0224h

Center Byte

0225h

High Byte

BIT 2

BIT 1

BIT 0

Note: There is only read access to this register.

Device Configuration Register Bitmap
ADDRESS

0226h

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

PART

0

0

0

0

0

0

0

0

DS2422

0

0

1

0

0

0

0

0

DS1923

0

1

0

0

0

0

0

0

DS1922L

0

1

1

0

0

0

0

0

DS1922T

1

0

0

0

0

0

0

0

DS1922E

Note: There is only read access to this register.

Password Control Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

0227h

BIT 3

BIT 2

BIT 1

BIT 0

EPW

Note: During a mission, there is only read access to this register.

Other Indicators

Security by Password

The Device Samples Counter register is similar to theMission Samples Counter register. During a mission thiscounter increments whenever the DS1922L/DS1922T
wake up to measure and log data and when thesedevices are testing for a temperature alarm in SUTA
mode. Between missions, the counter increments whenever the Forced Conversion command is executed. Thisway the Device Samples Counter register functions likea gas gauge for the battery that powers the device.
The Device Samples Counter register is reset to zero
when the device is assembled. The number format is
24-bit unsigned integer. The maximum number that canbe represented in this format is 16,777,215. Due to thecalibration and tests at the factory, new devices canhave a count value of up to 35,000. The typical value iswell below 10,000.
The code in the Device Configuration register allows
the master to distinguish between the DS2422 chip anddifferent versions of the DS1922 devices. The Device
Configuration Register Bitmap shows the codes
assigned to the various devices.

The DS1922L/DS1922T are designed to use two passwords that control read access and full access.
Reading from or writing to the scratchpad as well as theForced Conversion command does not require a password. The password must be transmitted immediately
after the command code of the memory or control function. If password checking is enabled, the password
transmitted is compared to the passwords stored in thedevice. The data pattern stored in the Password Control
register determines whether password checking isenabled.

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To enable password checking, the EPW bits need toform a binary pattern of 10101010 (AAh). The default
pattern of EPW is different from AAh. If the EPW patternis different from AAh, any pattern is accepted as longas it has a length of exactly 64 bits. Once enabled,changing the passwords and disabling password
checking requires the knowledge of the current fullaccess password.

Maxim Integrated | 25

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Read Access Password Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0228h

RP7

RP6

RP5

RP4

RP3

RP2

RP1

RP0

0229h

RP15

RP14

RP13

RP12

RP11

RP10

RP9

RP8

…

…

022Eh

RP55

RP54

RP53

RP52

RP51

RP50

RP49

RP48

022Fh

RP63

RP62

RP61

RP60

RP59

RP58

RP57

RP56

Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot bechanged while a mission is in progress.

Full Access Password Register Bitmap
ADDRESS

BIT 7

BIT 6

BIT 5

BIT 4

BIT 3

BIT 2

BIT 1

BIT 0

0230h

FP7

FP6

FP5

FP4

FP3

FP2

FP1

FP0

0231h

FP15

FP14

FP13

FP12

FP11

FP10

FP9

FP8

0236h

FP55

FP54

FP53

FP52

FP51

FP50

FP49

FP48

0237h

FP63

FP62

FP61

FP60

FP59

FP58

FP57

FP56

…

…

Note: There is only write access to this register. Attempting to read the password reports all zeros. The password cannot bechanged while a mission is in progress.

Before enabling password checking, passwords forread-only access as well as for full access(read/write/control) must be written to the password
registers. Setting up a password or enabling/disabling the password checking is done in the same
way as writing data to a memory location; only theaddress is different. Since they are located in thesame memory page, both passwords can be redefined at the same time.
The Read Access Password must be transmitted exactly in the sequence RP0, RP1…RP62, RP63. This password only applies to the Read Memory with CRC
function. The DS1922L/DS1922T deliver the requested
data only if the password transmitted by the master wascorrect or if password checking is not enabled.

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The full-access password must be transmitted exactly
in the sequence FP0, FP1…FP62, FP63. It affects thefunctions Read Memory with CRC, Copy Scratchpad,
Clear Memory, Start Mission, and Stop Mission. The
DS1922L/DS1922T execute the command only if thepassword transmitted by the master was correct or if
password checking is not enabled.
Due to the special behavior of the write-access logic,
the Password Control register and both passwords
must be written at the same time. When setting up new
passwords, always verify (read back) the scratchpad
before sending the Copy Scratchpad command. After a
new password is successfully copied from the scratchpad to its memory location, erase the scratchpad by filling it with new data (Write Scratchpad command).
Otherwise, a copy of the passwords remains in thescratchpad for public read access.

Maxim Integrated | 26

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

ETL = 1TLFS = 0

ETL = 1TLFS = 1
1000h

8192
8-BIT ENTRIESTEMPERATURE

1000h
WITH 16-BIT FORMAT,
THE MOST SIGNIFICANTBYTE IS STORED AT THE
LOWER ADDRESS.

4096
16-BIT ENTRIESTEMPERATURE

2FFFh

2FFFh

Figure 7. Temperature Logging

Data-Log Memory Usage
Once set up for a mission, the DS1922L/DS1922T log
the temperature measurements at equidistant time
points entry after entry in their data-log memory. The
data-log memory can store 8192 entries in 8-bit format
or 4096 entries in 16-bit format (Figure 7). In 16-bit format, the higher 8 bits of an entry are stored at the lower
address. Knowing the starting time point (Mission
Timestamp) and the interval between temperature measurements, one can reconstruct the time and date ofeach measurement.
There are two alternatives to the way the DS1922L/
DS1922T behave after the data-log memory is filledwith data. The user can program the device to either
stop any further recording (disable rollover) or overwrite
the previously recorded data (enable rollover), one
entry at a time, starting again at the beginning of therespective memory section. The contents of the Mission
Samples Counter in conjunction with the sample rate
and the Mission Timestamp allow reconstructing thetime points of all values stored in the data-log memory.
This gives the exact history over time for the mostrecent measurements taken. Earlier measurements
cannot be reconstructed.

Missioning
The typical task of the DS1922L/DS1922T is recording
temperature. Before the devices can perform this function, they need to be set up properly. This procedure iscalled missioning.
First, the DS1922L/DS1922T must have their RTC set toa valid time and date. This reference time can be thelocal time, or, when used inside of a mobile unit, UTC(also called GMT, Greenwich Mean Time), or any othertime standard that was agreed upon. The RTC oscillator
must be running (EOSC = 1). The memory assigned tostore the Mission Timestamp, Mission Samples
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Counter, and alarm flags must be cleared using theMemory Clear command. To enable the device for a
mission, the ETL bit must be set to 1. These are general
settings that must be made in any case, regardless ofthe type of object to be monitored and the duration of
the mission.
If alarm signaling is desired, the temperature alarm low
and high thresholds must be defined. See theTemperature Conversion section for how to convert atemperature value into the binary code to be written to
the threshold registers. In addition, the temperature
alarm must be enabled for the low and/or high threshold. This makes the device respond to a Conditional
Search command (see the 1-Wire ROM Function
Commands section), provided that an alarming condition has been encountered.
The setting of the RO bit (rollover enable) and sample
rate depends on the duration of the mission and themonitoring requirements. If the most recently logged
data is important, the rollover should be enabled (RO =1). Otherwise, one should estimate the duration of themission in minutes and divide the number by 8192
(8-bit format) or 4096 (16-bit format) to calculate thevalue of the sample rate (number of minutes between
conversions). For example, if the estimated duration ofa mission is 10 days (= 14400min), the 8192-byte
capacity of the data-log memory would be sufficient tostore a new 8-bit value every 1.8min (110s). If theDS1922L/DS1922T’s data-log memories are not large
enough to store all readings, one can use several
devices and set the Mission Start Delay to values thatmake the second device start logging as soon as thememory of the first device is full, and so on. The RO bit
must be set to 0 to disable rollover that would otherwise
overwrite the logged data.
After the RO bit and the Mission Start Delay are set, thesample rate must be written to the Sample Rate register. The sample rate can be any value from 1 to 16,383,
coded as an unsigned 14-bit binary number. The
fastest sample rate is one sample per second (EHSS =1, sample rate = 0001h) and the slowest is one sample
every 273.05hr (EHSS = 0, sample rate = 3FFFh). To
get one sample every 6min, for example, the sample
rate value must be set to 6 (EHSS = 0) or 360 decimal(equivalent to 0168h at EHSS = 1).
If there is a risk of unauthorized access to the DS1922L/
DS1922T or manipulation of data, one should define
passwords for read access and full access. Before thepasswords become effective, their use must be
enabled. See the Security by Password section for
more details.

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

The last step to begin a mission is to issue the Start
Mission command. As soon as they have received thiscommand, the DS1922L/DS1922T set the MIP flag andclear the MEMCLR flag. With the immediate/delayed
start mode (SUTA = 0), and after as many minutes as
specified by the Mission Start Delay are over, thedevice wakes up, copies the current date and time to
the Mission Timestamp register, and logs the first entryof the mission. This increments both the Mission
Samples Counter and Device Samples Counter. All
subsequent log entries are made as specified by thevalue in the Sample Rate register and the EHSS bit.
If the start upon temperature alarm mode is chosen(SUTA = 1) and temperature logging is enabled (ETL =1), the DS1922L/DS1922T first wait until the start delay
is over. Then the device wakes up in intervals as specified by the sample rate and EHSS bit and measures thetemperature. This increments the Device Samples
Counter register only. The first sample of the mission islogged when the temperature alarm occurred.
However, the Mission Samples Counter does not increment. One sample period later the Mission Timestamp
register is set. From then on, both the Mission Samples
Counter and Device Samples Counter registers increment at the same time. All subsequent log entries are
made as specified by the value in the Sample Rate register and the EHSS bit.
The general-purpose memory operates independentlyof the other memory sections and is not write protectedduring a mission. All the DS1922L/DS1922T’s memory

can be read at any time, e.g., to watch the progress ofa mission. Attempts to read the passwords read 00h
bytes instead of the data that is stored in the password
registers.

Memory Access
Address Registers and Transfer Status
Because of the serial data transfer, the DS1922L/
DS1922T employ three address registers called TA1,
TA2, and E/S (Figure 8). Registers TA1 and TA2 must
be loaded with the target address to which the data is
written or from which data is sent to the master upon a
Read command. Register E/S acts like a byte counterand 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 ofthe E/S register indicate the address of the last bytethat has been written to the scratchpad. This address iscalled ending offset. The DS1922L/DS1922T requirethat the ending offset is always 1Fh for a Copy
Scratchpad command to function. Bit 5 of the E/Sregister, called PF or partial byte flag, is set if the number of data bits sent by the master is not an integer
multiple of 8. Bit 6 is always a 0. Note that the lowest 5
bits of the target address also determine the address
within the scratchpad, where intermediate storage ofdata begins. This address is called byte offset. If thetarget address for a Write command is 13Ch, for example, the scratchpad stores incoming data beginning at
the byte offset 1Ch and is full after only 4 bytes. The

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 WITHDATA STATUS (E/S)(READ ONLY)

AA

0

PF

E4

E3

E2

E1

E0

Figure 8. Address Registers

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Maxim Integrated | 28

DS1922L/DS1922T

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 apage, i.e., the byte offset is 0. Thus, the full 32-byte
capacity of the scratchpad is available, resulting also in
the ending offset of 1Fh. The ending offset together with
the PF flag are a means to support the master checking
the data integrity after a Write command. The highest
valued bit of the E/S register, called authorization
accepted (AA), indicates that a valid Copy commandfor the scratchpad has been received and executed.
Writing data to the scratchpad clears this flag.

Writing with Verification
To write data to the DS1922L/DS1922T, the scratchpad
must be used as intermediate storage. First, the masterissues the Write Scratchpad command to specify thedesired 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 thescratchpad and to verify data integrity. As preamble tothe scratchpad data, the DS1922L/DS1922T send therequested 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 towrite data to the scratchpad. Similarly, a set AA flag
indicates that the Write command was not recognizedby the device. If everything went correctly, both flags
are cleared and the ending offset indicates the addressof the last byte written to the scratchpad. Now the master can continue verifying every data bit. After the master has verified the data, it must 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 DS1922L/DS1922T
have received these bytes, they copy the data to therequested location beginning at the target address.

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iButton Temperature Loggers
with 8KB Datalog Memory

Memory and Control
Function Commands
Figure 9 shows the protocols necessary for accessing
the memory and the special function registers of theDS1922L/DS1922T. An example on how to use theseand other functions to set up the DS1922L/DS1922T fora mission is included in the Mission Example: Prepare
and Start a New Mission section. The communication
between the master and the DS1922L/DS1922T takes
place either at standard speed (default, OD = 0) or at
overdrive speed (OD = 1). If not explicitly set into theoverdrive mode the DS1922L/DS1922T assume standard speed. Internal memory access during a mission
has priority over external access through the 1-Wireinterface. This affects several commands in this section. See the Memory Access Conflicts section for
details and solutions.

Write Scratchpad [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 is written to the scratchpad starting at the byte offset T[4:0]. The master must send as many bytes as areneeded to reach the ending offset of 1Fh. If a data byte
is incomplete, its content is ignored and the partial byte
flag PF is set.
When executing the Write Scratchpad command, theCRC generator inside the DS1922L/DS1922T calculates
a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by themaster (Figure 15). This CRC is generated using the
CRC-16 polynomial by first clearing the CRC generator
and then shifting in the command code (0Fh) of theWrite Scratchpad command, the target addresses TA1
and TA2 as supplied by the master, and all the databytes. If the ending offset is 11111b, the master cansend 16 read time slots and receive the inverted CRC16 generated by the DS1922L/DS1922T.
Note that both register pages are write protected during a mission. Although the Write Scratchpad commandworks normally at any time, the subsequent copy
scratchpad to a register page fails during a mission.

Maxim Integrated | 29

DS1922L/DS1922T

iButton Temperature Loggers
with 8KB Datalog Memory

Read Scratchpad [AAh]progress, write attempts to the register pages are notsuccessful. The AA bit remaining at 0 indicates this.

This command is used to verify scratchpad data andtarget address. After issuing the Read Scratchpad
command, the master begins reading. The first 2 bytes
are the target address. The next byte is the ending offset/data status byte (E/S) followed by the scratchpad
data beginning at the byte offset T[4:0], as shown in
Figure 8. The master can continue reading data until
the end of the scratchpad after which it receives aninverted CRC-16 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 reads logic 1s from theDS1922L/DS1922T until a reset pulse is issued.

Copy Scratchpad with Password [99h]This command is used to copy data from the scratchpad to the writable memory sections. After issuing the
Copy Scratchpad command, the master must provide a
3-byte authorization pattern, which can be obtained byreading the scratchpad for verification. This patternmust exactly match the data contained in the threeaddress registers (TA1, TA2, E/S, in that order). Next,
the master must transmit the 64-bit full-access password. If passwords are enabled and the transmitted
password is different from the stored full-access password, the Copy Scratchpad with Password command
fails. The device stops communicating and waits for a
reset pulse. If the password was correct or if passwords were not enabled, the device tests the 3-byte
authorization code. If the authorization code patternmatches, the AA flag is set and the copy begins. A pattern of alternating 1s and 0s is transmitted after thedata has been copied until the master issues a reset
pulse. While the copy is in progress, any attempt toreset the part is ignored. Copy typically takes 2µs perbyte.
The data to be copied is determined by the threeaddress registers. The scratchpad data from the beginning offset through the ending offset are copied, starting at the target address. The AA flag remains at logic
1 until it is cleared by the next Write Scratchpad command. With suitable password, the copy scratchpad
always functions for the 16 pages of data memory andthe 2 pages of calibration memory. While a mission is in

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Read Memory with Password andCRC [69h]
The Read Memory with CRC command is the generalfunction to read from the device. This command generates and transmits a 16-bit CRC following the last databyte of a memory page.
After having sent the command code of the Read
Memory with CRC command, the bus master sends a
2-byte address that indicates a starting byte location.
Next, the master must transmit one of the 64-bit passwords. If passwords are enabled and the transmitted
password does not match one of the stored passwords,
the Read Memory with Password and CRC command
fails. The device stops communicating and waits for a
reset pulse. If the password was correct or if passwords were not enabled, the master reads data fromthe DS1922L/DS1922T beginning from the starting
address and continuing until the end of a 32-byte pageis reached. At that point the bus master sends 16 additional read-data time slots and receives the inverted 16bit CRC. With subsequent read-data time slots themaster receives data starting at the beginning of thenext memory page followed again by the CRC for that
page. This sequence continues until the bus master
resets the device. When trying to read the passwords
or memory areas that are marked as “reserved,” theDS1922L/DS1922T transmit 00h or FFh bytes, respectively. The CRC at the end of a 32-byte memory page isbased on the data as it was transmitted.
With the initial pass through the read memory with CRC
flow, the 16-bit CRC value is the result of shifting thecommand byte into the cleared CRC generator followedby the two address bytes and the contents of the data
memory. Subsequent passes through the read memory
with CRC flow generate a 16-bit CRC that is the resultof clearing the CRC generator and then shifting in thecontents of the data memory page. After the 16-bit CRC
of the last page is read, the bus master receives logic
1s from the DS1922L/DS1922T until a reset pulse isissued. The Read Memory with CRC commandsequence can be ended at any point by issuing a reset
pulse.

Maxim Integrated | 30

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

FROM ROM FUNCTIONSFLOWCHART (FIGURE 11)

MASTER Tx MEMORY OR
CONTROL FUNCTION COMMAND

0Fh
WRITE SCRATCHPAD?

AAh
READ SCRATCHPAD?

N

Y

99h
COPY SCRATCHPAD[WITH PW]NYYMASTER Rx
TA1 [T7:T0]

MASTER Tx
TA1 [T7:T0]

TO FIGURE 9b

N

MASTER Tx
TA1 [T7:T0], TA2 [T15:T8]
AUTHORIZATION
CODE

MASTER Tx
TA2 [T15:T8]

MASTER Rx
TA2 [T15:T8]

MASTER Tx
E/S BYTE

DS1922 SETSSCRATCHPAD OFFSET = [T4:T0]
AND CLEARS (PF, AA)

MASTER Rx ENDING OFFSET
WITH DATA STATUS(E/S)

MASTER Tx
64 BITS [PASSWORD]

MASTER Tx DATA BYTETO SCRATCHPAD OFFSET

DS1922 SETSSCRATCHPAD OFFSET = [T4:T0]

PASSWORDACCEPTED?

NYDS1922 SETS [E4:E0] =SCRATCHPAD OFFSET

DS1922
INCREMENTSSCRATCHPADOFFSETMASTER Tx RESET?

MASTER Rx DATA BYTE FROMSCRATCHPAD OFFSET

DS1922
INCREMENTSSCRATCHPADOFFSETY

MASTER Tx RESET?

AUTHORIZATIONCODE MATCH?

N

Y

Y

AA = 1NN

SCRATCHPADOFFSET = 11111b?
Y

Y

N

MASTER Tx RESET?

NPARTIAL
BYTE WRITTEN?

YY
MASTER Rx CRC-16 OF
COMMAND, ADDRESS DATA,
E/S BYTE, AND DATA STARTING
AT THE TARGET ADDRESSNDS1922 COPIES SCRATCHPADDATA TO MEMORYSCRATCHPADOFFSET = 11111b?
MASTER Rx "1"s

MASTER Rx "1"sN

COPYINGFINISHEDMASTER Tx RESET?

YNNPF = 1
MASTER Rx CRC-16 OF
COMMAND, ADDRESS DATA

DS1922 Tx "0"Y

MASTER Tx RESET?

N
Y

MASTER Tx RESET?

Y

MASTER Tx RESET?

MASTER Rx "1"s

Y

N

N

DS1922 Tx "1"

MASTER Rx "1"sN

MASTER Tx RESET?
YFROM FIGURE 9b
TO ROM FUNCTIONSFLOWCHART (FIGURE 11)

Figure 9a. Memory/Control Function Flowchart

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Maxim Integrated | 31

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

69h
READ MEMORY [WITH
PW] AND CRC

FROM FIGURE 9a96h
CLEAR MEMORY[WITH PW]NYYDECISION MADE
BY DS1922

55h
FORCED CONVERSION?

N

MASTER Tx
TA1 [T7:T0], TA2 [T15:T8]

MASTER Tx
64 BITS [PASSWORD]

MASTER Tx
64 BITS [PASSWORD]

MASTER Tx
FFh DUMMY BYTEN

TO FIGURE 9c

Y
MASTER Tx
FFh DUMMY BYTEYMISSION IN
PROGRESS?
NPASSWORDACCEPTED?

NPASSWORDACCEPTED?

YDECISION MADE
BY MASTERMISSION IN
PROGRESS?

DS1922 COPIES RESULT TOADDRESS 020C/Dh

YN

MASTER Rx DATA BYTE FROMMEMORY ADDRESSNDS1922 CLEARSMISSION TIMESTAMP,MISSION SAMPLES COUNTER,
ALARM FLAGSDS1922
INCREMENTS
ADDRESS
COUNTERMASTER Tx RESET?

MASTER Tx RESET?
YDS1922 SETSMEMCLR = 1

N

END OF PAGE?

DS1922 PERFORMS A
TEMPERATURE CONVERSIONYDS1922 SETSMEMORY ADDRESS = [T15:T0]

Y

N

N
N

MASTER Tx RESET?

Y
Y

MASTER Rx CRC-16 OF
COMMAND, ADDRESS, DATA
(1ST PASS); CRC-16 OF DATA(SUBSEQUENT PASSES)MASTER Tx RESETNCRC OK?
Y

END OF MEMORY?

NYMASTER Rx "1"s
MASTER Tx RESET?

NY
TO FIGURE 9a

FROM FIGURE 9c

Figure 9b. Memory/Control Function Flowchart (continued)

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Maxim Integrated | 32

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

CCh
START MISSION[WITH PW]FROM FIGURE 9b

33h
STOP MISSION[WITH PW]NMISSION START
DELAY PROCESS

Y

N

Y

MASTER Tx
64 BITS [PASSWORD]

MASTER Tx
64 BITS [PASSWORD]
START DELAY
COUNTER = 0?

MASTER Tx
FFh DUMMY BYTEY
MASTER Tx
FFh DUMMY BYTE

N
DS1922 WAITS FOR 1 MINUTENPASSWORDACCEPTED?

PASSWORDACCEPTED?

DS1922 DECREMENTS
START DELAY COUNTER

Y

Y

Y

MISSION IN
PROGRESS?

SUTA = 1?

N

N

DS1922 WAITS ONESAMPLE PERIODYYMASTER Tx RESET?

MIP = 0?

N

MASTER Tx RESET?
Y

N

Y

N
DS1922 INITIATES MISSIONSTART DELAY PROCESSNDS1922 SETS
MIP = 0,WFTA = 0

MEMCLR = 1?

DS1922 SETS
MIP = 1,MEMCLR = 0

MISSION IN
PROGRESS?
YYDS1922 SETS WFTA = 1

NN

DS1922 PERFORMS 8-BIT
TEMPERATURE CONVERSIONTEMPERATURE
ALARM?

NY
DS1922 SETS WFTA = 0

DS1922 WAITS ONESAMPLE PERIOD

DS1922 COPIES RTC DATA TOMISSION TIMESTAMP REGISTERDS1922 STARTS LOGGINGTAKING FIRST SAMPLEEND OF PROCESSTO FIGURE 9b

Figure 9c. Memory/Control Function Flowchart (continued)

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Maxim Integrated | 33

DS1922L/DS1922T

iButton Temperature Loggers
with 8KB Datalog Memory

Clear Memory with Password [96h]Start Mission with Password [CCh]The Clear Memory with Password command is used toprepare the device for another mission. This commandis only executed if no mission is in progress. After thecommand code the master must transmit the 64-bit fullaccess password followed by an FFh dummy byte. If
passwords are enabled and the transmitted password
is different from the stored full-access password or a
mission is in progress, the Clear Memory with Password
command fails. The device stops communicating andwaits for a reset pulse. If the password was correct or if
passwords were not enabled, the device clears theMission Timestamp register, Mission Samples Counterregister, and all alarm flags of the Alarm Status register.
After these cells are cleared, the MEMCLR bit of theGeneral Status register reads 1 to indicate the successful execution of the Clear Memory with Password command. Clearing of the data-log memory is notnecessary because the Mission Samples Counter indicates how many entries in the data-log memory arevalid.

The DS1922L/DS1922T use a control function command to start a mission. A new mission can only be
started if the previous mission has been ended and thememory has been cleared. After the command code,
the master must transmit the 64-bit full-access password followed by an FFh dummy byte. If passwords areenabled and the transmitted password is different fromthe stored full-access password or a mission is inprogress, the Start Mission with Password command
fails. The device stops communicating and waits for a
reset pulse. If the password was correct or if passwords were not enabled, the device starts a mission. If
SUTA = 0, the sampling begins as soon as the Mission
Start Delay is over. If SUTA = 1, the first sample is written to the data-log memory at the time the temperature
alarm occurred. However, the Mission Samples Counter
does not increment. One sample period later, theMission Timestamp register is set and the regular sampling and logging begins. While the device is waiting
for a temperature alarm to occur, the WFTA flag in the
General Status register reads 1. During a mission there
is only read access to the register pages.

Forced Conversion [55h]
The Forced Conversion command can be used to measure the temperature without starting a mission. Afterthe command code, the master must send one FFhbyte to get the conversion started. The conversion
result is found as a 16-bit value in the Latest
Temperature Conversion Result register. This commandis only executed if no mission is in progress (MIP = 0).
It cannot be interrupted and takes maximum 600ms tocomplete. During this time memory access through the
1-Wire interface is blocked. The device behaves thesame way as during a mission when the sampling interferes with a memory/control function command. See theMemory Access Conflicts section for details.

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Stop Mission with Password [33h]
The DS1922L/DS1922T use a control function command to stop a mission. Only a mission that is inprogress can be stopped. After the command code,
the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords areenabled and the transmitted password is different fromthe stored full-access password or a mission is not inprogress, the Stop Mission with Password command
fails. The device stops communicating and waits for a
reset pulse. If the password was correct or if passwords were not enabled, the device clears the MIP bit
in the General Status register and restores write accessto the register pages. The WFTA bit is not cleared. See
the description of the General Status register for amethod to clear the WFTA bit.

Maxim Integrated | 34

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Memory Access Conflicts
While a mission is in progress or while the device iswaiting for a temperature alarm to start a mission, periodically a temperature sample is taken and logged.
This “internal activity” has priority over 1-Wire communication. As a consequence, device-specific commands(excluding ROM function commands and 1-Wire reset)
do not perform properly when internal and “external”
activities interfere with each other. Not affected are theStart Mission, Forced Conversion, and Clear Memorycommands, because they are not applicable while a

mission is in progress or while the device is waiting fora temperature alarm. Table 3 explains how the remaining five commands are affected by internal activity, how
to detect this interference, and how to work around it.
The interference is more likely to be seen with a highsample rate (one sample every second) and with highresolution logging, which can last up to 600ms. With
lower sample rates, interference may hardly be visibleat all. In any case, when writing driver software it isimportant to know about the possibility of interference
and to take measures to work around it.

Table 3. Memory Access Conflicts and Solutions
COMMAND

INDICATION OF INTERFERENCESOLUTION

Write Scratchpad

The CRC-16 at the end of the command flow reads
FFFFh.

Wait 0.5s, 1-Wire reset, address the device, repeat
Write Scratchpad with the same data, and check thevalidity of the CRC-16 at the end of the command
flow. Alternatively, use Read Scratchpad to verify
data integrity.

Read Scratchpad

The data read changes to FFh bytes or all bytes
received are FFh, including the CRC at the end of
the command flow.

Wait 0.5s, 1-Wire reset, address the device, repeat
Read Scratchpad, and check the validity of the
CRC-16 at the end of the command flow.

Copy Scratchpad

The device behaves as if the authorization code or
password was not valid or as if the copy function
would not end.

Wait 0.5s, 1-Wire reset, address the device, issue
Read Scratchpad, and check the AA bit of the E/S
byte. If the AA bit is set, Copy Scratchpad was
successful.

The data read changes to all FFh bytes or all bytes
Read Memory withreceived are FFh, including the CRC at the end of
CRC
the command flow, despite a valid password.

Wait 0.5s, 1-Wire reset, address the device, repeat
Read Memory with CRC, and check the validity of
the CRC-16 at the end of the memory page.

Stop Mission

The General Status register at address 0215h reads
FFh or the MIP bit is 1 while bits 0, 2, and 5 are 0.

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Wait 0.5s, 1-Wire reset, address the device, andrepeat Stop Mission. Perform a 1-Wire reset, address
the device, read the General Status register ataddress 0215h, and check the MIP bit. If the MIP bit
is 0, Stop Mission was successful.

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922Tof the pullup resistor primarily depends on the network
size and load conditions. The DS1922L/DS1922T
require a pullup resistor of maximum 2.2kΩ at any
speed.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is toresume. If this does not occur and the bus is left low for
more than 16µs (overdrive speed) or more than 120µs(standard speed), one or more devices on the bus may
be reset. Note that the DS1922L/DS1922T do not quite
meet the full 16µs maximum low time of the normal
1-Wire bus overdrive timing. With the DS1922L/
DS1922T, the bus must be left low for no longer than
12µs at overdrive to ensure that no DS1922L/DS1922T
on the 1-Wire bus performs a reset. The DS1922L/
DS1922T communicate properly when used in conjunction with a DS2480B or DS2490 1-Wire driver andadapters that are based on these driver chips.

1-Wire Bus System
The 1-Wire bus is a system that has a single bus masterand one or more slaves. In all instances theDS1922L/DS1922T are slave devices. The bus masteris typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling(signal types and timing). The 1-Wire protocol defines
bus transactions in terms of the bus state during specific time slots that are initiated on the falling edge of sync
pulses from the bus master.

Hardware Configuration
The 1-Wire bus has only a single line by definition; it isimportant that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device
attached to the 1-Wire bus must have open-drain or
three-state outputs. The 1-Wire port of the DS1922L/
DS1922T is open drain with an internal circuit equivalent to that shown in Figure 10.
A multidrop bus consists of a 1-Wire bus with multiple
slaves attached. At standard speed the 1-Wire bus
has a maximum data rate of 16.3kbps. The speed canbe boosted to 142kbps by activating the overdrive
mode. The DS1922L/DS1922T are not guaranteed to
be fully compliant to the iButton device standard.
Their maximum data rate in standard speed is
15.4kbps and 125kbps in overdrive speed. The value

Transaction Sequence
The protocol for accessing the DS1922L/DS1922T
through the 1-Wire port is as follows:• Initialization• ROM Function Command• Memory/Control Function Command• Transaction/Data

VPUP
BUS MASTER

DS1922L/DS1922T 1-Wire PORT
RPUP
DATA

Rx

Rx

IL

Tx

Tx

Rx = RECEIVE
Tx = TRANSMIT
OPEN-DRAIN
PORT PIN

100Ω MOSFET

Figure 10. Hardware Configurationwww.maximintegrated.com

Maxim Integrated | 36

DS1922L/DS1922T

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 bypresence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that theDS1922L/DS1922T are on the bus and are ready to operate. For more details, see the 1-Wire Signaling section.

1-Wire ROM Function Commands
Once the bus master has detected a presence, it canissue one of the eight ROM function commands that
DS1922L/DS1922T support. All ROM function commands are 8 bits long. A list of these commands follows(see the flowchart in Figure 11).

Read ROM [33h]This command allows the bus master to read theDS1922L/DS1922T’s 8-bit family code, unique 48-bit
serial number, and 8-bit CRC. This command can only
be used if there is a single slave on the bus. If morethan one slave is present on the bus, a data collisionoccurs when all slaves try to transmit at the same time
(open drain produces a wired-AND result). The resultant family code and 48-bit serial number results in amismatch of the CRC.

Match ROM [55h]The Match ROM command, followed by a 64-bit ROM
sequence, allows the bus master to address a specificDS1922L/DS1922T on a multidrop bus. Only theDS1922L/DS1922T that exactly matches the 64-bit
ROM sequence responds to the following memory function command. All other slaves wait for a reset pulse.
This command can be used with a single device or
multiple devices on the bus.

Search ROM [F0h]
When a system is initially brought up, the bus mastermight not know the number of devices on the 1-Wirebus or their registration numbers. By taking advantageof the wired-AND property of the bus, the master can

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iButton Temperature Loggers
with 8KB Datalog Memory

use a process of elimination to identify the registration
numbers of all slave devices. For each bit of the registration number, starting with the least significant bit, thebus master issues a triplet of time slots. On the first slot,
each slave device participating in the search outputs
the true value of its registration number bit. On the second slot, each slave device participating in the search
outputs the complemented value of its registration number bit. On the third slot, the master writes the true
value of the bit to be selected. All slave devices that do
not match the bit written by the master stop participating in the search. If both of the read bits are zero, themaster knows that slave devices exist with both statesof the bit. By choosing which state to write, the bus
master branches in the ROM code tree. After one complete pass, the bus master knows the registration number of a single device. Additional passes identify theregistration numbers of the remaining devices. Refer toApplication Note 187: 1-Wire Search Algorithm for a
detailed discussion, including an example.

Conditional Search ROM [ECh]The Conditional Search ROM command operates similarly to the Search ROM command except that only
those devices that fulfill certain conditions participate in
the search. This function provides an efficient means
for the bus master to identify devices on a multidrop
system that have to signal an important event. Aftereach pass of the conditional search that successfully
determined the 64-bit ROM code for a specific device
on the multidrop bus, that particular device can be individually accessed as if a Match ROM had been issued,
since all other devices have dropped out of the search
process and are waiting for a reset pulse.
The DS1922L/DS1922T respond to the conditional search
ROM command if one of the three alarm flags of the Alarm
Status register (address 0214h) reads 1. The temperature
alarm only occurs if enabled (see the Temperature Sensor
Alarm section). The BOR alarm is always enabled. The
first alarm that occurs makes the device respond to theConditional Search ROM command.

Maxim Integrated | 37

DS1922L/DS1922T

Skip ROM [CCh]This command can save time in a single-drop bus system by allowing the bus master to access the memory
functions without providing the 64-bit ROM code. For
example, if more than one slave is present on the bus
and a read command is issued following the Skip ROM
command, data collision occurs on the bus as multiple
slaves transmit simultaneously (open-drain pulldowns
produce a wired-AND result).

Resume [A5h]
The DS1922L/DS1922T must be accessed several times
before a mission starts. In a multidrop environment thismeans that the 64-bit ROM code after a Match ROM
command must be repeated for every access. To maximize the data throughput in a multidrop environment,
the Resume command was implemented. This command checks the status of the RC bit and, if it is set,
directly transfers control to the memory/control functions, similar to a Skip ROM command. The only way to
set the RC bit is through successfully executing the
Match ROM, Search ROM, or Overdrive-Match ROM
command. Once the RC bit is set, the device canrepeatedly be accessed through the Resume command
function. Accessing another device on the bus clears
the RC bit, preventing two or more devices from simultaneously responding to the Resume command.

Overdrive-Skip ROM [3Ch]
On a single-drop bus this command can save time byallowing the bus master to access the memory/control
functions without providing the 64-bit ROM code. Unlike
the normal Skip ROM command, the Overdrive-Skip

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iButton Temperature Loggers
with 8KB Datalog Memory

ROM command sets the DS1922L/DS1922T in the overdrive mode (OD = 1). All communication following thiscommand must occur at overdrive speed until a reset
pulse of minimum 690µs duration resets all devices on
the bus to standard speed (OD = 0).
When issued on a multidrop bus, this command sets all
overdrive-supporting devices into overdrive mode. To
subsequently address a specific overdrive-supporting
device, a reset pulse at overdrive speed must be
issued followed by a Match ROM or Search ROM command sequence. This speeds up the time for the
search process. If more than one slave supporting
overdrive is present on the bus and the Overdrive-Skip
ROM command is followed by a read command, data
collision occurs on the bus as multiple slaves transmit
simultaneously (open-drain pulldowns produce a wiredAND result).

Overdrive-Match ROM [69h]
The Overdrive-Match ROM command followed by a
64-bit ROM sequence transmitted at overdrive speed
allows the bus master to address a specific DS1922L/
DS1922T on a multidrop bus and to simultaneously set
it in overdrive mode. Only the DS1922L/DS1922T thatexactly matches the 64-bit ROM sequence respond to
the subsequent memory/control function command.
Slaves already in overdrive mode from a previous
Overdrive-Skip ROM or successful Overdrive-Match
ROM command remain in overdrive mode. All overdrive-capable slaves return to standard speed at thenext reset pulse of minimum 690µs duration. The
Overdrive-Match ROM command can be used with asingle or multiple devices on the bus.

Maxim Integrated | 38

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

BUS MASTER Tx
RESET PULSEFROM FIGURE 11b

FROM MEMORY/CONTROL FUNCTION
FLOWCHART (FIGURE 9)OD
RESET PULSE?

N

OD = 0Y
BUS MASTER Tx ROM
FUNCTION COMMAND

33h
READ ROM
COMMAND?

DS1922 Tx
PRESENCE PULSE

N

55h
MATCH ROM
COMMAND?

F0h
SEARCH ROM
COMMAND?

N

ECh
CONDITIONAL SEARCHCOMMAND?

N

Y

Y

Y

Y

RC = 0RC = 0RC = 0RC = 0N

N

TO FIGURE 11b

CONDITION
MET?
YDS1922 Tx
FAMILY CODE
(1 BYTE)DS1922 Tx BIT 0
MASTER Tx BIT 0

BIT 0 MATCH?

N

N

DS1922 Tx BIT 0

MASTER Tx BIT 0

MASTER Tx BIT 0

BIT 0 MATCH?

N

DS1922 Tx BIT 1
MASTER Tx BIT 1

BIT 1 MATCH?

N

N

DS1922 Tx BIT 1

DS1922 Tx BIT 1

DS1922 Tx BIT 1

MASTER Tx BIT 1

MASTER Tx BIT 1

BIT 1 MATCH?

N

Y

Y

MASTER Tx BIT 63

BIT 63 MATCH?

NN

BIT 1 MATCH?
Y

DS1922 Tx BIT 63
DS1922 Tx
CRC BYTE

BIT 0 MATCH?

YYY
DS1922 Tx
SERIAL NUMBER(6 BYTES)DS1922 Tx BIT 0

DS1922 Tx BIT 0

DS1922 Tx BIT 63

DS1922 Tx BIT 63

DS1922 Tx BIT 63

MASTER Tx BIT 63

MASTER Tx BIT 63

BIT 63 MATCH?

N

BIT 63 MATCH?

Y

Y

Y

RC = 1

RC = 1

RC = 1TO FIGURE 11b

FROM FIGURE 11b
TO MEMORY/CONTROL FUNCTION
FLOWCHART (FIGURE 9)

Figure 11a. ROM Functions Flowchart

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Maxim Integrated | 39

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

TO FIGURE 11a

FROM FIGURE 11a

CCh
SKIP ROM
COMMAND?

NY

A5h
RESUME
COMMAND?

3Ch
OVERDRIVESKIP ROM?

N

Y

N

Y

RC = 1?

NY

RC = 0; OD = 1

RC = 069h
OVERDRIVEMATCH ROM?

RC = 0; OD = 1

N

YMASTER Tx
RESET?

Y

MASTER Tx BIT 0

N(SEE NOTE)
MASTER Tx
RESET?
NY

BIT 0 MATCH?

N

OD = 0Y

MASTER Tx BIT 1(SEE NOTE)
BIT 1 MATCH?

N

OD = 0Y

MASTER Tx BIT 63(SEE NOTE)
BIT 63 MATCH?

N

OD = 0Y

FROM FIGURE 11a

RC = 1TO FIGURE 11a

NOTE: THE OD FLAG REMAINS AT 1 IF THE DEVICE WAS ALREADY AT OVERDRIVE SPEED BEFORE THE OVERDRIVE-MATCH ROM COMMAND WAS ISSUED.

Figure 11b. ROM Functions Flowchart (continued)

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Maxim Integrated | 40

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

drive mode and tRSTL is no longer than 80µs, the device
remains in overdrive mode.

Wire Signaling
The DS1922L/DS1922T require strict protocols to ensure
data integrity. The protocol consists of four types of signaling on one line: reset sequence with reset pulse andpresence pulse, write-zero, write-one, and read-data.
Except for the presence pulse, the bus master initiates
all these signals. The DS1922L/DS1922T can communicate at two different speeds: standard speed and overdrive speed. If not explicitly set into the overdrive mode,
the DS1922L/DS1922T communicate at standard
speed. While in overdrive mode the fast timing applies
to all waveforms.
To get from idle to active, the voltage on the 1-Wire line
needs to fall from VPUP below the threshold VTL. To getfrom active to idle, the voltage needs to rise from
VILMAX past the threshold VTH. The time it takes for thevoltage to make this rise is seen in Figure 12 as “ε” andits duration depends on the pullup resistor (RPUP) used
and the capacitance of the 1-Wire network attached.
The voltage V ILMAX is relevant for the DS1922L/
DS1922T when determining a logical level, not triggering any events.
The initialization sequence required to begin any communication with the DS1922L/DS1922T is shown in
Figure 12. A reset pulse followed by a presence pulse
indicates the DS1922L/DS1922T are ready to receive
data, given the correct ROM and memory function command. If the bus master uses slew-rate control on thefalling edge, it must pull down the line for tRSTL + tF tocompensate for the edge. A tRSTL duration of 690µs or
longer exits the overdrive mode, returning the device tostandard speed. If the DS1922L/DS1922T are in over-

After the bus master has released the line, it goes into
receive mode (Rx). Now the 1-Wire bus is pulled to
VPUP through the pullup resistor or, in the case of a
DS2480B driver, through active circuitry. When thethreshold VTH is crossed, the DS1922L/DS1922T wait
for tPDH and then transmit a presence pulse by pulling
the line low for tPDL. To detect a presence pulse, themaster must test the logical state of the 1-Wire line at
tMSP.
The tRSTH window must be at least the sum of tPDHMAX,t PDLMAX , and t RECMIN . Immediately after t RSTH is
expired, the DS1922L/DS1922T are ready for data communication. In a mixed population network, t RSTH
should be extended to minimum 480µs at standard
speed and 48µs at overdrive speed to accommodate
other 1-Wire devices.

Read/Write Time Slots
Data communication with the DS1922L/DS1922T 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 13.
All communication begins with the master pulling thedata line low. As the voltage on the 1-Wire line falls
below the threshold VTL, the DS1922L/DS1922T start
their internal timing generator that determines when thedata line is sampled during a write time slot and how
long data is valid during a read time slot.

MASTER Tx "RESET PULSE"MASTER Rx "PRESENCE PULSE"
ε

tMSP

VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tRSTL

tPDH

tF

tPDL

tREC
tRSTH

RESISTORMASTERDS1922L/DS1922T

Figure 12. Initialization Procedure: Reset and Presence Pulse

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Maxim Integrated | 41

DS1922L/DS1922T

Master-to-Slave
For a write-one time slot, the voltage on the data line
must have crossed the VTH threshold before the writeone low time tW1LMAX is expired. For a write-zero timeslot, the voltage on the data line must stay below the VTH
threshold until the write-zero low time tW0LMIN is expired.
The voltage on the data line should not exceed VILMAX
during the entire tW0L or tW1L window. After the VTH
threshold has been crossed, the DS1922L/DS1922T
need a recovery time tREC before they are ready for the
next time slot.

Slave-to-MasterA read-data time slot begins like a write-one time slot.
The voltage on the data line must remain below VTL
until the read low time tRL is expired. During the tRL
window, when responding with a 0, the DS1922L/
DS1922T start pulling the data line low; their internaltiming generator determines when this pulldown ends
and the voltage starts rising again. When responding
with a 1, the DS1922L/DS1922T do not hold the dataline low at all, and the voltage starts rising as soon astRL is over.
The sum of tRL + δ (rise time) on one side and the internal timing generator of the DS1922L/DS1922T on theother side define the master sampling window (tMSRMIN
to tMSRMAX) in which the master must perform a readfrom the data line. For most reliable communication, tRL
should be as short as permissible and the mastershould read close to but no later than tMSRMAX. Afterreading from the data line, the master must wait untiltSLOT is expired. This guarantees sufficient recovery
time tREC for the DS1922L/DS1922T to get ready for the
next time slot.

Improved Network Behavior(Switchpoint Hysteresis)
In a 1-Wire environment line termination is possible
only during transients controlled by the bus master(1-Wire driver). 1-Wire networks, therefore, are susceptible to noise of various origins. Depending on thephysical size and topology of the network, reflections
from end points and branch points can add up or cancel each other to some extent. Such reflections are visible as glitches or ringing on the 1-Wire communicationwww.maximintegrated.com

iButton Temperature Loggers
with 8KB Datalog Memory

line. Noise coupled onto the 1-Wire line from externalsources can also result in signal glitching. A glitch during the rising edge of a time slot can cause a slave
device to lose synchronization with the master and, asa consequence, result in a search ROM command
coming to a dead end or cause a device-specific function command to abort. For better performance in network applications, the DS1922L/DS1922T use a new
1-Wire front-end, which makes them less sensitive tonoise and also reduces the magnitude of noise injected by the slave device itself.
The DS1922L/DS1922T’s 1-Wire front-end differs fromtraditional slave devices in four characteristics:
1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to theline impedance than a digitally switched transistor,
converting the high-frequency ringing known fromtraditional devices into a smoother low-bandwidthtransition. The slew-rate control is specified by theparameter tFPD, which has different values for standard and overdrive speed.
2) There is additional lowpass filtering in the circuit that
detects the falling edge at the beginning of a timeslot. This reduces the sensitivity to high-frequency
noise. This additional filtering does not apply atoverdrive speed.
3) There is a hysteresis at the low-to-high switching
threshold VTH. If a negative glitch crosses VTH butdoes not go below VTH - VHY, it is not recognized(Figure 14, Case A). The hysteresis is effective atany 1-Wire speed.
4) There is a time window specified by the rising edgehold-off time tREH during which glitches are ignored,even if they extend below V TH - V HY threshold(Figure 14, Case B, t GL < t REH ). Deep voltage
droops or glitches that appear late after crossing the
VTH threshold and extend beyond the tREH window
cannot be filtered out and are taken as the beginning of a new time slot (Figure 14, Case C, tGL ≥tREH).
Devices that have the parameters tFPD, VHY, and tREH
specified in their electrical characteristics use theimproved 1-Wire front-end.

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

WRITE-ONE TIME SLOT
tW1L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V

ε

tF

tSLOT
RESISTORMASTERWRITE-ZERO TIME SLOT
tW0L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V

ε

tF

tREC

tSLOT
RESISTORMASTER

READ-DATA TIME SLOT
tMSR
tRL
VPUP
VIHMASTER
VTH

MASTERSAMPLING
WINDOWVTL
VILMAX
0V

δ

tF

tREC
tSLOT

RESISTORMASTERDS1922L/DS1922T

Figure 13. Read/Write Timing Diagrams

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

tREH

tREH

VPUP
VTH

VHY
CASE A

CASE BCASE C

0V
tGL

tGL

Figure 14. Noise Suppression Scheme

POLYNOMIAL = X16 + X15 + X2 + 1

1ST
STAGE
X0

X2

X1

9TH
STAGE
X8

3RD
STAGE

2ND
STAGE

10TH
STAGE
X9

11TH
STAGE
X10

4TH
STAGE
X3

12TH
STAGE
X11

5TH
STAGE
X4

13TH
STAGE
X12

6TH
STAGE
X5

14TH
STAGE
X13

7TH
STAGE
X6

8TH
STAGE
X7

15TH
STAGE
X14

16TH
STAGE
X15

X16

CRC OUTPUTINPUT DATA

Figure 15. CRC-16 Hardware Description and Polynomial

CRC Generation
The DS1922L/DS1922T use two types of CRCs. One
CRC is an 8-bit type and is stored in the most significant byte of the 64-bit ROM. The bus master can compute a CRC value from the first 56 bits of the 64-bit
ROM and compare it to the value stored within theDS1922L/DS1922T to determine if the ROM data has
been received error-free. The equivalent polynomial
function of this CRC is X8 + X5 + X4 + 1. This 8-bit CRC
is received in the true (noninverted) form, and it is computed at the factory and lasered into the ROM.
The other CRC is a 16-bit type, generated according to
the standardized CRC-16 polynomial function X16 + X15+ X2 + 1. This CRC is used for error detection whenreading register pages or the data-log memory using
the Read Memory with CRC command and for fast verification of a data transfer when writing to or readingfrom the scratchpad. In contrast to the 8-bit CRC, thewww.maximintegrated.com

16-bit CRC is always communicated in the inverted
form. A CRC generator inside the DS1922L/DS1922T(Figure 15) calculates a new 16-bit CRC as shown inthe command flowchart of Figure 9. The bus mastercompares the CRC value read from the device to theone it calculates from the data and decides whether tocontinue with an operation or to reread the portion of
the data with the CRC error. With the initial passthrough the Read Memory with CRC flowchart, the 16bit CRC value is the result of shifting the command byte
into the cleared CRC generator, followed by the two
address bytes and the data bytes. The password is
excluded from the CRC calculation. Subsequent passes through the Read Memory with CRC flowchart generate a 16-bit CRC that is the result of clearing the CRC
generator and then shifting in the data bytes.
With the Write Scratchpad command, the CRC is generated by first clearing the CRC generator and then shift-

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iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

ing in the command code, the target addresses TA1
and TA2, and all the data bytes. The DS1922L/DS1922T
transmit this CRC only if the data bytes written to thescratchpad include scratchpad ending offset 11111b.
The data can start at any location within the scratchpad.
With the Read Scratchpad command, the CRC is generated by first clearing the CRC generator and thenshifting in the command code, the target addresses
TA1 and TA2, the E/S byte, and the scratchpad data
starting at the target address. The DS1922L/DS1922T
transmit this CRC only if the reading continues throughthe end of the scratchpad, regardless of the actual
ending offset. For more information on generating CRC
values, refer to Application Note 27.

Command-Specific 1-Wire Communication Protocol—Legend
SYMBOLRSTPD

DESCRIPTION
1-Wire reset pulse generated by master.
1-Wire presence pulse generated by slave.

SelectCommand and data to satisfy the ROM function protocol.

WS

Command “Write Scratchpad.”RS

Command “Read Scratchpad.”

CPS

Command “Copy Scratchpad with Password.”

RMC

Command “Read Memory with Password and CRC.”

CM

Command “Clear Memory with Password.”FC

Command “Forced Conversion.”SM

Command “Start Mission with Password.”

STP

Command “Stop Mission with Password.”

TA

Target Address TA1, TA2.

TA-E/S

Target Address TA1, TA2 with E/S byte.

<Data to EOS>

Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh.

<Data to EOP>

Transfer of as many data bytes as are needed to reach the end of a memory page.

<Data to EOM>

Transfer of as many data bytes as are needed to reach the end of the data-log memory.

<PW/Dummy>

Transfer of 8 bytes that either represent a valid password or acceptable dummy data.

<32 Bytes>

Transfer of 32 bytes.

<Data>

Transfer of an undetermined amount of data.

FFh

Transmission of one FFh byte.

CRC-16

Transfer of an inverted CRC-16.

FF LoopIndefinite loop where the master reads FF bytes.

AA LoopBusy

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Indefinite loop where the master reads AA bytes.
Interval during Copy Scratchpad where the DS1922L/T does not respond. Any bits read during thistime are logic 1.

Maxim Integrated | 45

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Command-Specific 1-Wire Communication Protocol—Color Codes
Master-to-Slave

Slave-to-Master1-Wire Communication Examples
Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)RST PD Select WSTA<Data to EOS>

CRC-16FF Loop

Read Scratchpad (Cannot Fail)RST PD Select RS

TA-E/S <Data to EOS>

CRC-16FF Loop

Copy Scratchpad with Password (Success)
RST PD Select CPS TA-E/S<PW/Dummy>Busy

AA Loop

Copy Scratchpad with Password (Fail TA-E/S or Password)
RST PD Select CPS TA-E/S<PW/Dummy>

FF Loop

Read Memory with Password and CRC (Success)
RST PD Select RMC TA<PW/Dummy><Data to EOP>

CRC-16<32 Bytes>

CRC-16FF Loop

Loop

Read Memory with Password and CRC (Fail Password or Address)
RST PD Select RMC TA<PW/Dummy>

FF LoopClear Memory with Password
RST PD Select CM<PW/Dummy>FFh

FF Loop

To verify success, read the General Status register at address 0215h. If MEMCLR is 1, the command was
executed successfully.

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Maxim Integrated | 46

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

1-Wire Communication Examples (continued)
Forced Conversion
RST PD Select FC

FFh

FF Loop

To read the result and to verify success, read the addresses 020Ch to 020Fh (results) and the Device Samples
Counter at address 0223h to 0225h. If the count has incremented, the command was executed successfully.
Start Mission with Password
RST PD Select SM<PW/Dummy>FFh

FF Loop

To verify success, read the General Status register at address 0215h. If MIP is 1 and MEMCLR is 0, the command
was executed successfully.
Stop Mission with Password
RST PD Select STP<PW/Dummy>FFh

FF Loop

To verify success, read the General Status register at address 0215h. If MIP is 0, the command was executed
successfully.

Step 1: Clear the data of the previous mission.

Mission Example: Prepare
and Start a New Mission

Step 2: Write the setup data to register page 1.
Step 3: Start the new mission.

Assumption: The previous mission has been ended byusing the Stop Mission command. Passwords are notenabled. The device is a DS1922L.
Starting a mission requires three steps:
MASTER MODE

Step 1: Clear the data of the previous mission.
With only a single device connected to the bus master,
the communication of step 1 looks like this:

DATA (LSB FIRST)

Tx(Reset)Rx(Presence)

Tx

CCh

Tx

96h

Tx

<8 FFh bytes>

Tx

FFh

Tx

(Reset)Rx(Presence)

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COMMENTS
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Clear Memory” command
Send dummy password
Send dummy byte
Reset pulse
Presence pulse

Maxim Integrated | 47

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Step 2: Write the setup data to register page 1.
During the setup, the device needs to learn the following information:• Time and Date
• Sample Rate
• Alarm Thresholds
ADDRESS

DATA

0200h

00h

0201h

30h

0202h

15h

0203h

01h

0204h

04h

0205h

02h

0206h

0Ah

0207h

00h

0208h

52h

0209h

66h

020Ah

00h

020Bh

FFh

020Ch

FFh

020Dh

FFh

020Eh

FFh

020Fh

FFh

• Alarm Controls (Response to Conditional Search)• General Mission Parameters (e.g., Channels to Log
and Logging Format, Rollover, Start Mode)• Mission Start Delay
The following data sets up the DS1922L for a missionthat logs temperature using 8-bit format.

EXAMPLE VALUESFUNCTION

15:30:00 hoursTime

1st of April in 2002

Date

Every 10 minutes (EHSS = 0)

Sample rate

0°C low
10°C highTemperature Alarm Thresholds(Don’t care)(Not applicable with DS1922L/DS1922T)(Don’t care)

Clock through read-only registers

0210h

02h

Enable high alarm

Temperature Alarm Control

0211h

FCh

Disabled(Not applicable with DS1922L/DS1922T)

0212h

01h

On (enabled), EHSS = 0 (low sample rate)

RTC Oscillator Control, sample rate selection

0213h

C1h

Normal start; no rollover; 8-bit temperature log

General Mission Control

0214h

FFh

0215h

FFh

(Don’t care)

Clock through read-only registers

0216h

5Ah

0217h

00h

90 minutes

Mission Start Delay

0218h

00h

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Maxim Integrated | 48

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

With only a single device connected to the bus master,
the communication of step 2 looks like this:MASTER MODEDATA (LSB FIRST)

Tx(Reset)COMMENTS

Rx(Presence)

Tx

CCh

Issue “Skip ROM” command

Tx

0Fh

Issue “Write Scratchpad” command

Tx

00h

TA1, beginning offset = 00h

Tx

02h

Tx

<25 Data Bytes>

Write 25 bytes of data to scratchpad

Tx<7 FFh Bytes>

Write through the end of the scratchpad

Tx(Reset)Rx(Presence)

Tx

CCh

Issue “Skip ROM” command

Tx

AAh

Issue “Read Scratchpad” command

Rx

00h

Read TA1, beginning offset = 00h

Rx

02h

Read TA2, address = 0200h

Rx

1Fh

Rx

<32 Data Bytes>

Reset pulse
Presence pulse

TA2, address = 0200h

Reset pulse
Presence pulse

Read E/S, ending offset = 1Fh, flags = 0h
Read scratchpad data and verify

Tx(Reset)Rx(Presence)

Tx

CCh

Tx

99h

Issue “Copy Scratchpad” command

Tx

00h

TA1

Tx

02h

TA2

Tx

1Fh

E/S

Tx

<8 FFh Bytes>

Tx(Reset)Rx(Presence)Issue “Skip ROM” command(AUTHORIZATION CODE)

Send dummy password
Reset pulse
Presence pulse

If step 3 was successful, the MIP bit in the General
Status register is 1, the MEMCLR bit is 0, and theMission Start Delay counts down.

Step 3: Start the new mission.
With only a single device connected to the bus master,
the communication of step 3 looks like this:MASTER MODE

Reset pulse
Presence pulse

DATA (LSB FIRST)COMMENTS

Tx(Reset)Rx(Presence)

Tx

CCh

Issue “Skip ROM” command

Tx

CCh

Issue “Start Mission” command

Tx<8 FFh Bytes>

Tx

FFh

Tx

(Reset)Rx(Presence)

www.maximintegrated.com

Reset pulse
Presence pulse

Send dummy password
Send dummy byte
Reset pulse
Presence pulse

Maxim Integrated | 49

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

The correction algorithm consists of two steps: preparation and execution. By means of the family code thepreparation step verifies whether the device actually is
a DS1922. Then the configuration byte is checked to
identify the type of DS1922 (L or T). If it is the correct
device, the data for software correction is read andconverted from binary to decimal °C format. Next,
three coefficients A, B, and C are computed. In theexecution step, the temperature reading as deliveredby the DS1922 is first converted from the lowbyte/high-byte format (TcL, TcH) to °C (Tc) and thencorrected to TCORR. Once step 1 is performed, thethree coefficients can be used repeatedly to correct
any temperature reading and temperature log of thesame device.

Software Correction Algorithm
for Temperature
The accuracy of high-resolution temperature conversion results (forced conversion as well as temperaturelogs) can be improved through a correction algorithm.
The data needed for this software correction is stored
in the calibration memory (memory page 18, duplicatedin page 19). This data consists of reference temperature (Tr) and conversion result (Tc) for two different temperatures. See the Temperature Conversion section forthe binary number format.
The software correction algorithm requires two additional values, which are not stored in the device. These
values, Tr1 and Offset, are derived from the device
configuration byte.
ADDRESSDESIGNATOR

0240h

Tr2H

Cold-reference temperature, high byte

DESCRIPTION

0241h

Tr2L

Cold-reference temperature, low byte

0242h

Tc2H

Conversion result at cold-reference temperature, high byte

0243h

Tc2L

Conversion result at cold-reference temperature, low byte

0244h

Tr3H

Hot-reference temperature, high byte

0245h

Tr3L

Hot-reference temperature, low byte

0246h

Tc3H

Conversion result at hot-reference temperature, high byte

0247h

Tc3L

Conversion result at hot-reference temperature, low byte

Step 1. Preparation
Read the 64-bit ROM to obtain the family code. If family code ≠ 41h, then stop (wrong device).
Read the configuration byte at address 0226h.
If code = 40h, then Tr1 = 60, Offset = 41 (DS1922L)
If code = 60h, then Tr1 = 90, Offset = 1 (DS1922T)
For all other codes, stop (wrong device).
Tr2 = Tr2H/2 + Tr2L/512 - Offset (convert from binary to °C)
Tr3 = Tr3H/2 + Tr3L/512 - Offset (convert from binary to °C)
Tc2 = Tc2H/2 + Tc2L/512 - Offset (convert from binary to °C)
Tc3 = Tc3H/2 + Tc3L/512 - Offset (convert from binary to °C)
Err2 = Tc2 - Tr2
Err3 = Tc3 - Tr3
Err1 = Err2
B = (Tr22 - Tr12) x (Err3 - Err1)/[(Tr22 - Tr12) x (Tr3 - Tr1) + (Tr32 - Tr12) x (Tr1 - Tr2)]
A = B x (Tr1 - Tr2) / (Tr22 - Tr12)
C = Err1 - A x Tr12 - B x Tr1
Step 2. Execution
TC = TcH/2 + TcL/512 - Offset (convert from binary to °C)
TCORR = Tc - (A x Tc2 + B x Tc + C) (the actual correction)www.maximintegrated.com

Maxim Integrated | 50

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Pin Configuration• Rugged Chip-Based Data Carrier with Fast, Simple

F5 SIZE

Access to Information• Digital Identification and Information by
Momentary Contact• Unique Factory-Lasered 64-Bit Registration
Number Ensures Error-Free Device Selection
and Absolute Traceability Because No Two Parts
Are Alike• Built-In Multidrop Controller for 1-Wire Net• Chip-Based Data Carrier Compactly Stores
Information• Data Can Be Accessed While Affixed to an Object• Button Shape is Self-Aligning with Cup-Shaped
Probes• Durable Stainless-Steel Case Engraved with
Registration Number Withstands Harsh
Environments• Easily Affixed with Self-Stick Adhesive Backing,Latched by Its Flange, or Locked with a Ring
Pressed Onto Its Rim• Presence Detector Acknowledges When Reader
First Applies Voltage—

Tr2 = -10.1297°C

Err2 = 0.0672°C

Tr3 = 24.6483°C

Err3 = -0.1483°C

Tc2 = -10.0625°C

Err1 = 0.0672°C

Tc3 = 24.5°C—

RESULTING CORRECTION
COEFFICIENTSAPPLICATION OF
CORRECTION
COEFFICIENTS TO SAMPLEREADING

B = -0.008741—

A = 0.000175/°C

TC = 22.500°C

C = -0.039332°C

TCORR = 22.647°C

iB

ut

t o n ®. com

Tr1 = 60°C

ERROR VALUESBRANDING

A1

16.25mm

41

000000FBC52B
0

1-Wire® ®
W Thermochron L #ZZZ D S1922

W

CONVERTED DATA FROMCALIBRATION MEMORY

0.51mmYY

Numerical Correction Example

5.89mmF5

Common iButton Device Features

17.35mm

IO
GND

Package Information
For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but thedrawing pertains to the package regardless of RoHS status.
PACKAGETYPE

PACKAGECODEOUTLINENO.

LAND
PATTERN NO.

F5 CanIB#6CB

21-0266—

Note: The software correction requires floating-point arithmetic(24 bit or better). Suitable math libraries for microcontrollers arefound on various websites and are included in cross compilers.
Thermochron is a registered trademark of Maxim Integrated Products, Inc.

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Maxim Integrated | 51

iButton Temperature Loggers
with 8KB Datalog Memory

DS1922L/DS1922T

Revision History
REVISIONNUMBER

7

REVISIONDATE

DESCRIPTIONPAGESCHANGED

12/07

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 Application section: Note that the initial
sealing level of DS1922L/DS1922T achieves IP56. Aging and use conditions candegrade 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 watertightenclosure that has been rated to IP68 (See www.maximintegrated.com/AN4126)

1, 4, 128

4/09

Created newer template-styled data sheet

All

9

10/09

Deleted the standard part numbers from the Ordering Information table

1

10

4/11

Updated UL certificate reference; deleted  from the tW1L specification in the Electrical
Characteristics table; applied note 14 to the tW0L specification in the Electrical
Characteristics table; added more details to Electrical Characteristics table notes 5,14, and 15; revised the last sentence of the Parasite Power section for more clarity;
added paragraph on validation certificates to Detailed Description section; added
more details on the Device Samples Counter in the Other Indicators section

1, 3, 4, 13, 25

11

6/13

Removed the UL 913 5th Ed. Compliance statement from the Common iButton Device
Features section and iButton Can Physical Specification table; reworded the Electrical
Characteristics table Note 19

1, 4

12

11/13

Added the Busy state during Copy Scratchpad to the Command-Specific 1-WireCommunication Protocol—Legend and 1-Wire Communication Examples sections

45, 4613

3/15

Updated Benefits and Features and Common iButton Device Features section

1, 51

For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated’s website at www.maximintegrated.com.

Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent
licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min andmax limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance.
Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc.

© 2015 Maxim Integrated Products, Inc. | 52