Maxim DS1922L-F5 Temperature logger ibutton with 8kb data-log memory Datasheet

19-4990; Rev 10; 4/11
Temperature Logger iButton with 8KB
Data-Log Memory
The DS1922L/DS1922T temperature logger iButtons® 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 application-specific
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. Each DS1922L/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
Features
♦ Automatically Wakes Up, Measures Temperature,
and Stores Values in 8KB of Data-Log Memory in
8-Bit or 16-Bit Format
♦ Digital Thermometer Measures Temperature with
8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution
♦ 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
♦ Water Resistant or Waterproof if Placed Inside
DS9107 iButton Capsule (Exceeds Water
Resistant 3 ATM Requirements)
♦ 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
♦ Quick Access to Alarmed Devices Through 1-Wire
Conditional Search Function
♦ 512 Bytes of General-Purpose Memory Plus 64
Bytes of Calibration Memory
♦ Two-Level Password Protection of All Memory
and Configuration Registers
♦ 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
♦ Operating Temperature Range: DS1922L: -40°C to
+85°C; DS1922T: 0°C to +125°C
Common iButton Features
♦ 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 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
♦ Meets UL 913, 5th Ed., Rev. 1997-02-24; Intrinsically
Safe Apparatus: Approved Under Entity Concept
for Use in Class I, Division 1, Group A, B, C, and D
Locations
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
DS1922L-F5#
-40°C to +85°C
F5 iButton
DS1922T-F5#
0°C to +125°C
F5 iButton
#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
DS9092
iButton Probe
Pin Configuration appears at end of data sheet.
iButton and 1-Wire are registered trademarks of Maxim Integrated Products, Inc.
________________________________________________________________ Maxim Integrated Products
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1
DS1922L/DS1922T
General Description
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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
SYMBOL
TA
CONDITIONS
MIN
TYP
MAX
DS1922L (Note 1)
-40
+85
DS1922T (Note 1)
0
+125
UNITS
°C
IO PIN: GENERAL DATA
1-Wire Pullup Resistance
RPUP
Input Capacitance
CIO
Input Load Current
IL
(Notes 2, 3)
(Note 4)
IO pin at VPUP
High-to-Low Switching Threshold
VTL
(Notes 5, 6)
Input 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 Time
Time-Slot Duration (Note 2)
tREC
tREH
t SLOT
2.2
Standard speed, RPUP = 2.2k
Overdrive speed, RPUP = 2.2k
Overdrive speed, directly prior to reset
pulse; RPUP = 2.2k
k
100
800
pF
6
10
μA
3.2
V
0.4
0.3
V
0.7
3.4
V
0.09
N/A
V
0.4
V
5
2
μs
5
(Note 11)
0.6
Standard speed
65
Overdrive speed, VPUP > 4.5V
Overdrive speed (Note 12)
8
2.0
μs
μs
9.5
IO PIN: 1-Wire RESET, PRESENCE-DETECT CYCLE
Reset Low Time (Note 2)
Presence-Detect High Time
Presence-Detect Fall Time
(Note 13)
2
tRSTL
t PDH
tFPD
Standard speed, VPUP > 4.5V
Standard speed (Note 12)
480
720
690
720
Overdrive speed, VPUP > 4.5V
48
80
Overdrive speed (Note 12)
70
80
Standard speed, VPUP > 4.5V
15
60
Standard speed (Note 12)
15
63.5
Overdrive speed (Note 12)
2
7
Standard speed, VPUP > 4.5V
1.5
5
Standard speed
1.5
8
Overdrive speed
0.15
1
_______________________________________________________________________________________
μs
μs
μs
Temperature Logger iButton with 8KB
Data-Log Memory
(VPUP = +3.0V to +5.25V.)
PARAMETER
Presence-Detect Low Time
Presence-Detect Sample Time
(Note 2)
SYMBOL
t PDL
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)
Overdrive speed (Note 12)
7
24
7
28
Standard speed, VPUP > 4.5V
65
75
Standard speed
71.5
75
Overdrive speed
8
9
Standard speed
60
120
Overdrive Speed, VPUP > 4.5V (Note 12)
6
12
7.5
12
UNITS
μs
μs
IO PIN: 1-Wire WRITE
Write-Zero Low Time
(Notes 2, 14)
tW0L
Overdrive speed (Note 12)
Write-One Low Time
(Notes 2, 14)
tW1L
Standard speed
5
15
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
5
15 - Overdrive speed
1
1.95 - Standard speed
tRL + 15
Overdrive speed
tRL + 1.95
μs
μs
REAL-TIME CLOCK
See RTC Accuracy
graphs
Accuracy
Frequency Deviation
F
-40°C to +85°C
-300
+60
0°C to +125°C
-600
+60
min/
month
PPM
TEMPERATURE CONVERTER
Conversion Time
(Note 16)
tCONV
Thermal Response Time
Constant (Note 17)
RESP
Conversion Error Without
Software Correction
Conversion Error with Software
Correction
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
Note 6:
8-bit mode
30
75
16-bit mode (11 bits)
240
600
iButton package
ms
130
s
(Notes 18, 19)
See Temperature
Accuracy graphs
°C
(Notes 19, 20)
See Temperature
Accuracy graphs
°C
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.
_______________________________________________________________________________________
3
DS1922L/DS1922T
ELECTRICAL CHARACTERISTICS (continued)
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
ELECTRICAL CHARACTERISTICS (continued)
(VPUP = +3.0V to +5.25V.)
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
Note 16:
Note 17:
Note 18:
Note 19:
Note 20:
The voltage on IO must be less than or equal to VILMAX whenever the master drives the line low.
Voltage above which, during a rising edge on IO, a logic 1 is detected.
After VTH is crossed during a rising edge on IO, the voltage on IO must drop by VHY to be detected as logic 0.
The I-V characteristic is linear for voltages less than 1V.
The earliest recognition of a negative edge is possible at tREH after VTH has been previously reached.
Numbers in bold are not in compliance with the published iButton standards. See the Comparison Table.
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.
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.
δ in Figure 13 represents the time required for the pullup circuitry to pull the voltage on IO up from VIL to the input-high
threshold of the bus master. The actual maximum duration for the master to pull the line low is tRLMAX + tF.
To conserve battery power, use 8-bit temperature logging whenever possible.
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.
Includes +0.1/-0.2°C calibration chamber measurement uncertainty.
Warning: Not for use as the sole method of measuring or tracking temperature in products and articles that could affect
the health or safety of persons, plants, animals, or other living organisms, including but not limited to foods, beverages,
pharmaceuticals, medications, blood and blood products, organs, flammable, and combustible products. User shall
assure that redundant (or other primary) methods of testing and determining the handling methods, quality, and fitness of
the articles and products should be implemented. Temperature tracking with this product, where the health or safety of the
aforementioned persons or things could be adversely affected, is only recommended when supplemental or redundant
information sources are used. Data-logger products are 100% tested and calibrated at time of manufacture by Maxim to
ensure that they meet all data sheet parameters, including temperature accuracy. User shall be responsible for proper use
and storage of this product. As with any sensor-based product, user shall also be responsible for occasionally rechecking
the temperature accuracy of the product to ensure it is still operating properly.
Assumes using calibration memory with calibration equations for error compensation. Includes +0.1/-0.2°C calibration
chamber measurement uncertainty. Guaranteed by design.
COMPARISON TABLE
LEGACY VALUES
STANDARD SPEED
(μs)
PARAMETER
DS1922L/DS1922T VALUES
OVERDRIVE 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 standards.
iButton CAN PHYSICAL SPECIFICATION
SIZE
See the Package Information section.
WEIGHT
Ca. 3.3 grams
SAFETY
Meets UL 913, 5th Ed., Rev. 1997-02-24; Intrinsically Safe Apparatus, approval under Entity Concept for use in
Class I, Division 1, Group A, B, C, and D Locations.
4
_______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
EVERY MINUTE
NO SAMPLES
EVERY 10 MINUTES
EVERY 60 MINUTES
EVERY 3 MINUTES
OSCILLATOR 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 MINUTE
NO SAMPLES
EVERY 10 MINUTES
EVERY 60 MINUTES
EVERY 3 MINUTES
OSCILLATOR OFF
EVERY 30 MINUTES
EVERY 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)
_______________________________________________________________________________________
5
DS1922L/DS1922T
DS1922L Minimum Product Lifetime vs. Temperature, Slow Sampling
Temperature Logger iButton with 8KB
Data-Log Memory
DS1922L/DS1922T
DS1922L Minimum Product Lifetime vs. Temperature, Fast Sampling
EVERY SECOND
EVERY 30 SECONDS
EVERY 10 SECONDS
EVERY 3 SECONDS
EVERY 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 SECONDS
EVERY 10 SECONDS
EVERY 3 SECONDS
EVERY 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)
6
_______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
EVERY MINUTE
EVERY 60 MINUTES
EVERY 10 MINUTES
OSCILLATOR OFF
EVERY 3 MINUTES
NO SAMPLES
10
8-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 MINUTES
EVERY 10 MINUTES
OSCILLATOR OFF
EVERY 3 MINUTES
NO SAMPLES
EVERY 30 MINUTES
EVERY 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)
_______________________________________________________________________________________
7
DS1922L/DS1922T
DS1922T Minimum Product Lifetime vs. Temperature, Slow Sampling
Temperature Logger iButton with 8KB
Data-Log Memory
DS1922L/DS1922T
DS1922T Minimum Product Lifetime vs. Temperature, Fast Sampling
EVERY SECOND
EVERY 30 SECONDS
EVERY 10 SECONDS
EVERY 3 SECONDS
EVERY 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 SECONDS
EVERY 10 SECONDS
EVERY 3 SECONDS
EVERY 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)
8
_______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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
_______________________________________________________________________________________
9
DS1922L/DS1922T
DS1922L Minimum Product Lifetime vs. Sample Rate
Temperature Logger iButton with 8KB
Data-Log 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
MINUTES BETWEEN SAMPLES
10
______________________________________________________________________________________
100
Temperature Logger iButton with 8KB
Data-Log Memory
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
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
90
100
110
120
TEMPERATURE (°C)
NOTE: THE GRAPHS ARE BASED ON 11-BIT DATA.
______________________________________________________________________________________
11
DS1922L/DS1922T
DS1922L Temperature Accuracy
Temperature Logger iButton with 8KB
Data-Log Memory
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
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
80
90
100
110
120
TEMPERATURE (°C)
12
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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 refrigerators
and freezers. With its shifted temperature range, the
DS1922T is suited to monitor processes that require
temperatures close to the boiling point of water, such
as pasteurization of food items. Note that the initial sealing level of the DS1922L/DS1922T achieves the equivalent of IP56. Aging and use conditions can degrade the
integrity of the seal over time, so for applications with
significant exposure to liquids, sprays, or other similar
environments, it is recommended to place the
DS1922L/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 of
iButton Data Loggers and Capsules ). Software for
setup and data retrieval through the 1-Wire interface is
available for free download from the iButton website
(www.ibutton.com). This software also includes drivers
for the serial and USB port of a PC and routines to
access 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 the
DS1922L, DS1922T, DS1922E, and DS1923 (temperature portion only) data loggers. Input is the iButton’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 the
DS1922L/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
and another one for a read/write password, can only be
written, never read.
Figure 2 shows the hierarchical structure of the 1-Wire
protocol. The bus master must first provide one of the
eight ROM function commands: Read ROM, Match
ROM, Search ROM, Conditional Search ROM, Skip
ROM, Overdrive-Skip ROM, Overdrive-Match ROM, or
Resume. 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 for
these 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 the
eight 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.
Parasite Power
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever
the IO input is high. IO provides sufficient power as
long 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 not
consumed for 1-Wire ROM function commands, and
2) if the battery is exhausted for any reason, the ROM
may still be read normally. The remaining circuitry of
the DS1922 is solely operated by battery energy.
64-Bit Lasered ROM
Each DS1922L/DS1922T contains a unique ROM code
that 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 the
first 56 bits (see Figure 3 for details). The 1-Wire CRC is
generated using a polynomial generator consisting of a
shift register and XOR gates as shown in Figure 4. The
polynomial is X8 + X5 + X4 + 1. Additional information
about the 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, starting
with 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. After
the last bit of the serial number has been entered, the
shift register contains the CRC value. Shifting in the 8
bits of CRC returns the shift register to all 0s.
______________________________________________________________________________________
13
DS1922L/DS1922T
Detailed Description
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
1-Wire PORT
ROM
FUNCTION
CONTROL
IO
64-BIT
LASERED
ROM
MEMORY
FUNCTION
CONTROL
3V LITHIUM
PARASITE-POWERED
CIRCUITRY
256-BIT
SCRATCHPAD
DS1922L
DS1922T
GENERAL-PURPOSE
SRAM
(512 BYTES)
INTERNAL
TIMEKEEPING,
CONTROL REGISTERS,
AND COUNTERS
32.768kHz
OSCILLATOR
THERMAL
SENSE
REGISTER PAGES
(64 BYTES)
CALIBRATION MEMORY
(64 BYTES)
ADC
CONTROL
LOGIC
DATA-LOG MEMORY
8KB
Figure 1. Block Diagram
14
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
DS1922L/DS1922T
1-Wire NET
BUS
MASTER
OTHER DEVICES
DS1922L/DS1922T
COMMAND LEVEL:
AVAILABLE COMMANDS:
DATA FIELD AFFECTED:
1-Wire ROM
FUNCTION COMMANDS
READ ROM
MATCH ROM
SEARCH ROM
CONDITIONAL SEARCH ROM
SKIP ROM
RESUME
OVERDRIVE-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-FLAG
RC-FLAG
RC-FLAG, OD-FLAG
64-BIT ROM, RC-FLAG, OD-FLAG
WRITE SCRATCHPAD
READ SCRATCHPAD
COPY 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, PASSWORDS
MEMORY, REGISTERS, PASSWORDS
MISSION TIMESTAMP, MISSION SAMPLES COUNTER,
START DELAY, ALARM FLAGS, PASSWORDS
MEMORY ADDRESSES 020Ch TO 020Dh
FLAGS, TIMESTAMP, MEMORY ADDRESSES
020Ch TO 020Dh (WHEN LOGGING)
FLAGS
DS1922L/DS1922T-SPECIFIC
MEMORY/CONTROL FUNCTION
COMMANDS
FORCED CONVERSION
START 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
______________________________________________________________________________________
15
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Memory
Figure 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 the
device 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 page
that acts as a buffer when writing to the SRAM memory
or the register pages. The data memory can be written
at any time. The calibration memory holds data from the
device calibration that can be used to further improve
the accuracy of 11-bit temperature readings. See the
Software Correction Algorithm for Temperature section
for details. The last byte of the calibration memory page
stores 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 not
recommended. See the Security by Password section
for ways to protect the memory. The access type for the
register pages is register-specific and depends on
whether 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 the
write 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
SCRATCHPAD
ADDRESS
0000h TO 001Fh
32-BYTE GENERAL-PURPOSE SRAM
(R/W)
PAGE 0
0020h TO 01FFh
GENERAL-PURPOSE SRAM (R/W)
PAGES 1 TO 15
0200h TO 021Fh
32-BYTE REGISTER PAGE 1
PAGE 16
0220h TO 023Fh
32-BYTE REGISTER PAGE 2
PAGE 17
0240h TO 025Fh
CALIBRATION MEMORY PAGE 1 (R/W)
PAGE 18
0260h TO 027Fh
CALIBRATION MEMORY PAGE 2 (R/W)
PAGE 19
0280h 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
16
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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
Months
R/W
R
Sample
Rate
R/W
R
Temperature
Alarms
R/W
R
—
R/W
R
Latest
Temperature
R
R
—
R
R
Single Years
Low Byte
0
High Byte
0208h
Low Threshold
0209h
High 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
DS1922L/DS1922T
ADDRESS
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
Mission
Control
0214h
BOR
1
1
1
0
0
THF
TLF
Alarm Status
R
R
0215h
1
1
0
WFTA
MEMCLR
0
MIP
0
General
Status
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
______________________________________________________________________________________
17
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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 Date
0
BIT 1
Single Date
10
Months
BIT 0
FUNCTION
ACCESS*
Mission
Timestamp
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
Mission
Samples
Counter
0223h
Low Byte
0224h
Center Byte
R
R
0225h
High Byte
Device
Samples
Counter
0226h
Configuration Code
Flavor
R
R
0227h
EPW
PW Control
R/W
R
0228h
First Byte
…
…
W
—
022Fh
Eighth Byte
Read
Access
Password
0230h
First Byte
…
…
W
—
0237h
Eighth Byte
Full
Access
Password
(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)
18
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
Timekeeping and Calendar
The RTC and calendar information is accessed by
reading/writing the appropriate bytes in the register
page, address 0200h to 0205h. For readings to be
valid, all RTC registers must be read sequentially starting at address 0200h. Some of the RTC bits are set to
0. These bits always read 0 regardless of how they are
written. The number representation of the 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. When
high, the 12hr mode is selected. In the 12hr mode, bit 5
is 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 is
either 00 or a multiple of 4, the device adds a 29th of
February. 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 and
the longest time is 273.05hr (sample rate = 3FFFh). The
EHSS bit is located in the RTC Control register at
address 0212h. It is important that the user sets the
EHSS bit accordingly while setting the Sample Rate
register. Writing a sample rate of 0000h results in a
sample 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 Date
0
BIT 0
Single 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.
______________________________________________________________________________________
19
DS1922L/DS1922T
Detailed Register Descriptions
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Temperature Conversion
This equation is valid for converting temperature readings stored in the data-log memory as well as for data
read from the Latest Temperature Conversion Result
register. The “-41” applies to the DS1922L. For the
DS1922T, 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 and
ends 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 and
0.0625°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 equivalent
of 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 the
Temperature 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
DECIMAL
HEX
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
41.000
16-Bit
17h
23
60h
96
-29.3125
10.6875
Table 2. Temperature Alarm Threshold Examples
(°C)
20
TALM (DS1922T)
(°C)
TALM (DS1922L)
HEX
DECIMAL
HEX
DECIMAL
65.5
85h
133
25.5
85h
133
30.0
3Eh
62
-10.0
3Eh
62
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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 the
alarm signaling is enabled. The bits ETLA and ETHA
that enable the temperature alarm are located in the
Temperature Sensor Control register. The temperature
alarm flags TLF and THF are found in the Alarm Status
register at address 0214h.
Bit 1: Enable Temperature High Alarm (ETHA). This
bit controls whether, during a mission, the temperature
high alarm flag (THF) can be set, if a temperature conversion results in a value equal to or higher than the
value in the Temperature High Alarm Threshold register.
If ETHA is 1, temperature high alarms are enabled. If
ETHA is 0, temperature high alarms are not generated.
Bit 0: Enable Temperature Low Alarm (ETLA). This
bit controls whether, during a mission, the temperature
low alarm flag (TLF) can be set, if a temperature conversion results in a value equal to or lower than the
value in the Temperature Low Alarm Threshold register.
If ETLA is 1, temperature low alarms are enabled. If
ETLA is 0, temperature low alarms are not generated.
To minimize the power consumption of the DS1922L/
DS1922T, the RTC oscillator should be turned off when
these devices are not in use. The oscillator on/off bit is
located in the RTC Control register. This register also
includes the EHSS bit, which determines whether the
sample rate is specified in seconds or minutes.
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. When
set 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, the
oscillator 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 to
logic 1.
______________________________________________________________________________________
21
DS1922L/DS1922T
Temperature Sensor Control Register Bitmap
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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 the
DS1922L/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, the
device 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 the
alarm occurred. However, the mission sample counter
does not increment. This functionality is guaranteed by
design and not production tested.
22
Bit 4: Rollover Control (RO). This bit controls whether,
during a mission, the data-log memory is overwritten
with new data or whether data logging is stopped once
the data-log memory is full. Setting this bit to 1 enables
the rollover and data logging continues at the beginning, overwriting previously collected data. If this bit is
0, the logging and conversions stop once the data-log
memory is full. However, the RTC continues to run and
the MIP bit remains set until the Stop Mission command
is 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 is
0, the data is stored in 8-bit format. If this bit is 1, the
16-bit format is used (higher resolution). With 16-bit format, the most significant byte is stored at the lower
address.
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.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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
0
MIP
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 iButtons, the devices that encountered an
alarm can quickly be identified by means of the
Conditional 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 the
host 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 this
bit reads 1, the Mission Start Upon Temperature Alarm
was selected and the Start Mission command was successfully executed, but the device has not yet experienced the temperature alarm. This bit is cleared after a
temperature alarm event, but is not affected by the
Clear Memory command. Once set, WFTA remains set
if a mission is stopped before a temperature alarm
occurs. To clear WFTA manually before starting a new
mission, set the high temperature alarm (address
0209h) to -40°C and perform a forced conversion.
Bit 3: Memory Cleared (MEMCLR). If this bit reads 1,
the Mission Timestamp, Mission Samples Counter, and
all the alarm flags of the Alarm Status register have
been cleared in preparation of a new mission.
Executing the Clear Memory command clears these
memory sections. The MEMCLR bit returns to 0 as soon
as a new mission is started by using the Start Mission
command. The memory must be cleared for a mission
to start.
Bit 1: Mission in Progress (MIP). If this bit reads 1, the
device has been set up for a mission and this mission is
still in progress. The MIP bit returns from logic 1 to logic
0 when a mission is ended. See the Start Mission with
Password and Stop Mission with Password sections.
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.
______________________________________________________________________________________
23
DS1922L/DS1922T
Alarm Status Register Bitmap
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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
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
BIT 2
BIT 1
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 Date
0
BIT 0
Single 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
0222h
High 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 register
tells how many minutes must expire from the time a
mission was started until the first measurement of the
mission 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 to
store all readings at the selected sample rate, one can
use several devices and set the Mission Start Delay for
the second device to start recording as soon as the
memory of the first device is full, and so on. The RO bit
in the Mission Control register (address 0213h) must be
set to 0 to prevent overwriting of collected data once
the data-log memory is full.
The Mission Timestamp register indicates the date and
time of the first temperature sample of the mission.
There is only read access to the Mission Timestamp
register.
24
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 the
Data-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.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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 the
Mission Samples Counter register. During a mission this
counter increments whenever the DS1922L/DS1922T
wake up to measure and log data and when these
devices are testing for a temperature alarm in SUTA
mode. Between missions, the counter increments whenever the Forced Conversion command is executed. This
way the Device Samples Counter register functions like
a gas gauge for the battery that powers the iButton.
The Device Samples Counter register is reset to zero
when the iButton is assembled. The number format is
24-bit unsigned integer. The maximum number that can
be represented in this format is 16,777,215. Due to the
calibration and tests at the factory, new devices can
have a count value of up to 35,000. The typical value is
well below 10,000.
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 the
Forced 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 the
device. The data pattern stored in the Password Control
register determines whether password checking is
enabled.
To enable password checking, the EPW bits need to
form a binary pattern of 10101010 (AAh). The default
pattern of EPW is different from AAh. If the EPW pattern
is different from AAh, any pattern is accepted as long
as it has a length of exactly 64 bits. Once enabled,
changing the passwords and disabling password
checking requires the knowledge of the current fullaccess password.
The code in the Device Configuration register allows
the master to distinguish between the DS2422 chip and
different versions of the DS1922 iButtons. The Device
Configuration Register Bitmap shows the codes
assigned to the various devices.
______________________________________________________________________________________
25
DS1922L/DS1922T
Device Samples Counter Register Bitmap
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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 be
changed 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 be
changed while a mission is in progress.
Before enabling password checking, passwords for
read-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 the
address is different. Since they are located in the
same 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 was
correct or if password checking is not enabled.
26
The full-access password must be transmitted exactly
in the sequence FP0, FP1…FP62, FP63. It affects the
functions Read Memory with CRC, Copy Scratchpad,
Clear Memory, Start Mission, and Stop Mission. The
DS1922L/DS1922T execute the command only if the
password transmitted by the master was correct or if
password checking is not enabled.
Due to the special behavior of the write-access logic,
the Password Control register and both passwords
must be written at the same time. When setting up new
passwords, always verify (read back) the scratchpad
before sending the Copy Scratchpad command. After a
new password is successfully copied from the scratchpad to its memory location, erase the scratchpad by filling it with new data (Write Scratchpad command).
Otherwise, a copy of the passwords remains in the
scratchpad for public read access.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
ETL = 1
TLFS = 1
1000h
8192
8-BIT ENTRIES
TEMPERATURE
1000h
4096
16-BIT ENTRIES
TEMPERATURE
2FFFh
WITH 16-BIT FORMAT,
THE MOST SIGNIFICANT
BYTE IS STORED AT THE
LOWER ADDRESS.
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 of
each measurement.
There are two alternatives to the way the DS1922L/
DS1922T behave after the data-log memory is filled
with data. The user can program the device to either
stop any further recording (disable rollover) or overwrite
the previously recorded data (enable rollover), one
entry at a time, starting again at the beginning of the
respective memory section. The contents of the Mission
Samples Counter in conjunction with the sample rate
and the Mission Timestamp allow reconstructing the
time points of all values stored in the data-log memory.
This gives the exact history over time for the most
recent measurements taken. Earlier measurements
cannot be reconstructed.
Missioning
The typical task of the DS1922L/DS1922T iButtons is
recording temperature. Before the devices can perform
this function, they need to be set up properly. This procedure is called missioning.
First, the DS1922L/DS1922T must have their RTC set to
a valid time and date. This reference time can be the
local time, or, when used inside of a mobile unit, UTC
(also called GMT, Greenwich Mean Time), or any other
time standard that was agreed upon. The RTC oscillator
must be running (EOSC = 1). The memory assigned to
store the Mission Timestamp, Mission Samples
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 the
passwords become effective, their use must be
enabled. See the Security by Password section for
more details.
______________________________________________________________________________________
27
DS1922L/DS1922T
ETL = 1
TLFS = 0
Counter, and alarm flags must be cleared using the
Memory 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 of
the 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 the
Temperature Conversion section for how to convert a
temperature 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 the
monitoring requirements. If the most recently logged
data is important, the rollover should be enabled (RO =
1). Otherwise, one should estimate the duration of the
mission in minutes and divide the number by 8192
(8-bit format) or 4096 (16-bit format) to calculate the
value of the sample rate (number of minutes between
conversions). For example, if the estimated duration of
a mission is 10 days (= 14400min), the 8192-byte
capacity of the data-log memory would be sufficient to
store a new 8-bit value every 1.8min (110s). If the
DS1922L/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 that
make the second device start logging as soon as the
memory 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, the
sample 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).
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
The last step to begin a mission is to issue the Start
Mission command. As soon as they have received this
command, the DS1922L/DS1922T set the MIP flag and
clear 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, the
device wakes up, copies the current date and time to
the Mission Timestamp register, and logs the first entry
of the mission. This increments both the Mission
Samples Counter and Device Samples Counter. All
subsequent log entries are made as specified by the
value in the Sample Rate register and the EHSS bit.
If the start upon temperature alarm mode is chosen
(SUTA = 1) and temperature logging is enabled (ETL =
1), the 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 the
temperature. This increments the Device Samples
Counter register only. The first sample of the mission is
logged 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 independently
of the other memory sections and is not write protected
during a mission. All the DS1922L/DS1922T’s memory
can be read at any time, e.g., to watch the progress of
a 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 counter
and Transfer Status register. It is used to verify data
integrity with Write commands. Therefore, the master
only has read access to this register. The lower 5 bits of
the E/S register indicate the address of the last byte
that has been written to the scratchpad. This address is
called ending offset. The DS1922L/DS1922T require
that the ending offset is always 1Fh for a Copy
Scratchpad command to function. Bit 5 of the E/S
register, called PF or partial byte flag, is set if the number of data bits sent by the master is not an integer
multiple of 8. Bit 6 is always a 0. Note that the lowest 5
bits of the target address also determine the address
within the scratchpad, where intermediate storage of
data begins. This address is called byte offset. If the
target address for a Write command is 13Ch, for example, 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 WITH
DATA STATUS (E/S)
(READ ONLY)
AA
0
PF
E4
E3
E2
E1
E0
Figure 8. Address Registers
28
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
Writing with Verification
To write data to the DS1922L/DS1922T, the scratchpad
must be used as intermediate storage. First, the master
issues the Write Scratchpad command to specify the
desired target address, followed by the data to be written to the scratchpad. In the next step, the master
sends the Read Scratchpad command to read the
scratchpad and to verify data integrity. As preamble to
the scratchpad data, the DS1922L/DS1922T send the
requested target address TA1 and TA2 and the contents of the E/S register. If the PF flag is set, data did
not arrive correctly in the scratchpad. The master does
not need to continue reading; it can start a new trial to
write data to the scratchpad. Similarly, a set AA flag
indicates that the Write command was not recognized
by the device. If everything went correctly, both flags
are cleared and the ending offset indicates the address
of the last byte written to the scratchpad. Now the master can continue verifying every data bit. After the master has verified the data, it 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 the
requested location beginning at the target address.
Memory and Control
Function Commands
Figure 9 shows the protocols necessary for accessing
the memory and the special function registers of the
DS1922L/DS1922T. An example on how to use these
and other functions to set up the DS1922L/DS1922T for
a 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 the
overdrive mode the DS1922L/DS1922T assume standard speed. Internal memory access during a mission
has priority over external access through the 1-Wire
interface. 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 are
needed 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, the
CRC 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 the
master (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 the
Write Scratchpad command, the target addresses TA1
and TA2 as supplied by the master, and all the data
bytes. If the ending offset is 11111b, the master can
send 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 command
works normally at any time, the subsequent copy
scratchpad to a register page fails during a mission.
______________________________________________________________________________________
29
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 a
page, 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 command
for the scratchpad has been received and executed.
Writing data to the scratchpad clears this flag.
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Read Scratchpad [AAh]
This command is used to verify scratchpad data and
target address. After issuing the Read Scratchpad
command, the master begins reading. The first 2 bytes
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 an
inverted 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 the
DS1922L/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 by
reading the scratchpad for verification. This pattern
must exactly match the data contained in the three
address registers (TA1, TA2, E/S, in that order). Next,
the master must transmit the 64-bit full-access password. If passwords are enabled and the transmitted
password is different from the stored full-access password, the Copy Scratchpad with Password command
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 pattern
matches, the AA flag is set and the copy begins. A pattern of alternating 1s and 0s is transmitted after the
data has been copied until the master issues a reset
pulse. While the copy is in progress, any attempt to
reset the part is ignored. Copy typically takes 2µs per
byte.
The data to be copied is determined by the three
address registers. The scratchpad data from the beginning offset through the ending offset 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 and
the 2 pages of calibration memory. While a mission is in
30
progress, write attempts to the register pages are not
successful. The AA bit remaining at 0 indicates this.
Read Memory with Password and
CRC [69h]
The Read Memory with CRC command is the general
function to read from the device. This command generates and transmits a 16-bit CRC following the last data
byte of a memory page.
After having sent the command code of the Read
Memory with CRC command, the bus master sends a
2-byte address that indicates a starting byte location.
Next, the master must transmit one of the 64-bit passwords. If passwords are enabled and the transmitted
password does not match one of the stored passwords,
the Read Memory with Password and CRC command
fails. The device stops communicating and waits for a
reset pulse. If the password was correct or if passwords were not enabled, the master reads data from
the DS1922L/DS1922T beginning from the starting
address and continuing until the end of a 32-byte page
is reached. At that point the bus master sends 16 additional read-data time slots and receives the inverted 16bit CRC. With subsequent read-data time slots the
master receives data starting at the beginning of the
next memory page followed again by the CRC for that
page. This sequence continues until the bus master
resets the device. When trying to read the passwords
or memory areas that are marked as “reserved,” the
DS1922L/DS1922T transmit 00h or FFh bytes, respectively. The CRC at the end of a 32-byte memory page is
based on the data as it was transmitted.
With the initial pass through the read memory with CRC
flow, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator followed
by the 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 result
of clearing the CRC generator and then shifting in the
contents of the data memory page. After the 16-bit CRC
of the last page is read, the bus master receives logic
1s from the DS1922L/DS1922T until a reset pulse is
issued. The Read Memory with CRC command
sequence can be ended at any point by issuing a reset
pulse.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
0Fh
WRITE SCRATCHPAD?
DS1922L/DS1922T
FROM ROM FUNCTIONS
FLOWCHART (FIGURE 11)
MASTER Tx MEMORY OR
CONTROL FUNCTION COMMAND
AAh
READ SCRATCHPAD?
N
Y
99h
COPY SCRATCHPAD
[WITH PW]
N
Y
Y
MASTER 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 SETS
SCRATCHPAD OFFSET = [T4:T0]
AND CLEARS (PF, AA)
MASTER Rx ENDING OFFSET
WITH DATA STATUS
(E/S)
MASTER Tx
64 BITS [PASSWORD]
MASTER Tx DATA BYTE
TO SCRATCHPAD OFFSET
DS1922 SETS
SCRATCHPAD OFFSET = [T4:T0]
PASSWORD
ACCEPTED?
N
Y
DS1922 SETS [E4:E0] =
SCRATCHPAD OFFSET
DS1922
INCREMENTS
SCRATCHPAD
OFFSET
MASTER Tx RESET?
MASTER Rx DATA BYTE FROM
SCRATCHPAD OFFSET
DS1922
INCREMENTS
SCRATCHPAD
OFFSET
Y
MASTER Tx RESET?
AUTHORIZATION
CODE MATCH?
N
Y
Y
AA = 1
N
N
SCRATCHPAD
OFFSET = 11111b?
Y
Y
N
MASTER Tx RESET?
N
PARTIAL
BYTE WRITTEN?
Y
Y
MASTER Rx CRC-16 OF
COMMAND, ADDRESS DATA,
E/S BYTE, AND DATA STARTING
AT THE TARGET ADDRESS
N
DS1922 COPIES SCRATCHPAD
DATA TO MEMORY
SCRATCHPAD
OFFSET = 11111b?
MASTER Rx "1"s
MASTER Rx "1"s
N
COPYING
FINISHED
MASTER Tx RESET?
Y
N
N
PF = 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"s
N
MASTER Tx RESET?
Y
FROM FIGURE 9b
TO ROM FUNCTIONS
FLOWCHART (FIGURE 11)
Figure 9a. Memory/Control Function Flowchart
______________________________________________________________________________________
31
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
69h
READ MEMORY [WITH
PW] AND CRC
FROM FIGURE 9a
96h
CLEAR MEMORY
[WITH PW]
N
Y
Y
DECISION 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 BYTE
N
TO FIGURE 9c
Y
MASTER Tx
FFh DUMMY BYTE
MISSION IN
PROGRESS?
Y
N
PASSWORD
ACCEPTED?
N
PASSWORD
ACCEPTED?
Y
DECISION MADE
BY MASTER
MISSION IN
PROGRESS?
DS1922 COPIES RESULT TO
ADDRESS 020C/Dh
Y
N
MASTER Rx DATA BYTE FROM
MEMORY ADDRESS
N
DS1922 CLEARS
MISSION TIMESTAMP,
MISSION SAMPLES COUNTER,
ALARM FLAGS
DS1922
INCREMENTS
ADDRESS
COUNTER
MASTER Tx RESET?
MASTER Tx RESET?
Y
DS1922 SETS
MEMCLR = 1
N
END OF PAGE?
DS1922 PERFORMS A
TEMPERATURE CONVERSION
Y
DS1922 SETS
MEMORY 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 RESET
N
CRC OK?
Y
END OF MEMORY?
N
Y
MASTER Rx "1"s
MASTER Tx RESET?
N
Y
TO FIGURE 9a
Figure 9b. Memory/Control Function Flowchart (continued)
32
______________________________________________________________________________________
FROM FIGURE 9c
Temperature Logger iButton with 8KB
Data-Log Memory
33h
STOP MISSION
[WITH PW]
N
MISSION START
DELAY PROCESS
Y
DS1922L/DS1922T
CCh
START MISSION
[WITH PW]
FROM FIGURE 9b
N
Y
MASTER Tx
64 BITS [PASSWORD]
MASTER Tx
64 BITS [PASSWORD]
START DELAY
COUNTER = 0?
MASTER Tx
FFh DUMMY BYTE
Y
MASTER Tx
FFh DUMMY BYTE
N
DS1922 WAITS FOR 1 MINUTE
N
PASSWORD
ACCEPTED?
PASSWORD
ACCEPTED?
DS1922 DECREMENTS
START DELAY COUNTER
Y
Y
Y
MISSION IN
PROGRESS?
SUTA = 1?
N
N
DS1922 WAITS ONE
SAMPLE PERIOD
Y
Y
MASTER Tx RESET?
MIP = 0?
N
MASTER Tx RESET?
Y
N
Y
N
DS1922 INITIATES MISSION
START DELAY PROCESS
N
DS1922 SETS
MIP = 0,
WFTA = 0
MEMCLR = 1?
DS1922 SETS
MIP = 1,
MEMCLR = 0
MISSION IN
PROGRESS?
Y
Y
DS1922 SETS WFTA = 1
N
N
DS1922 PERFORMS 8-BIT
TEMPERATURE CONVERSION
TEMPERATURE
ALARM?
N
Y
DS1922 SETS WFTA = 0
DS1922 WAITS ONE
SAMPLE PERIOD
DS1922 COPIES RTC DATA TO
MISSION TIMESTAMP REGISTER
DS1922 STARTS LOGGING
TAKING FIRST SAMPLE
END OF PROCESS
TO FIGURE 9b
Figure 9c. Memory/Control Function Flowchart (continued)
______________________________________________________________________________________
33
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Clear Memory with Password [96h]
Start Mission with Password [CCh]
The Clear Memory with Password command is used to
prepare the device for another mission. This command
is only executed if no mission is in progress. After the
command code the master must transmit the 64-bit 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 and
waits for a reset pulse. If the password was correct or if
passwords were not enabled, the device clears the
Mission Timestamp register, Mission Samples Counter
register, and all alarm flags of the Alarm Status register.
After these cells are cleared, the MEMCLR bit of the
General Status register reads 1 to indicate the successful execution of the Clear Memory with Password command. Clearing of the data-log memory is not
necessary because the Mission Samples Counter indicates how many entries in the data-log memory are
valid.
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 the
memory 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 are
enabled and the transmitted password is different from
the stored full-access password or a mission is in
progress, the Start Mission with Password command
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, the
Mission 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. After
the command code, the master must send one FFh
byte to get the conversion started. The conversion
result is found as a 16-bit value in the Latest
Temperature Conversion Result register. This command
is only executed if no mission is in progress (MIP = 0).
It cannot be interrupted and takes maximum 600ms to
complete. During this time memory access through the
1-Wire interface is blocked. The device behaves the
same way as during a mission when the sampling interferes with a memory/control function command. See the
Memory Access Conflicts section for details.
34
Stop Mission with Password [33h]
The DS1922L/DS1922T use a control function command to stop a mission. Only a mission that is in
progress can be stopped. After the command code,
the master must transmit the 64-bit full-access password followed by a FFh dummy byte. If passwords are
enabled and the transmitted password is different from
the stored full-access password or a mission is not in
progress, the Stop Mission with Password command
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 access
to the register pages. The WFTA bit is not cleared. See
the description of the General Status register for a
method to clear the WFTA bit.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
While a mission is in progress or while the device is
waiting 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 the
Start Mission, Forced Conversion, and Clear Memory
commands, because they are not applicable while a
mission is in progress or while the device is waiting for
a 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 visible
at all. In any case, when writing driver software it is
important to know about the possibility of interference
and to take measures to work around it.
Table 3. Memory Access Conflicts and Solutions
COMMAND
INDICATION OF INTERFERENCE
SOLUTION
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 the
validity 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 with
received are FFh, including the CRC at the end of
CRC
the command flow, despite a valid password.
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.
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.
Wait 0.5s, 1-Wire reset, address the device, and
repeat Stop Mission. Perform a 1-Wire reset, address
the device, read the General Status register at
address 0215h, and check the MIP bit. If the MIP bit
is 0, Stop Mission was successful.
______________________________________________________________________________________
35
DS1922L/DS1922T
Memory Access Conflicts
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
1-Wire Bus System
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 1-Wire bus is a system that has a single bus master
and one or more slaves. In all instances the
DS1922L/DS1922T are slave devices. The bus master
is typically a microcontroller. The discussion of this bus
system is broken down into three topics: hardware configuration, transaction sequence, and 1-Wire signaling
(signal types and timing). The 1-Wire protocol defines
bus transactions in terms of the bus state during specific time slots that are initiated on the falling edge of sync
pulses from the bus master.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus
must be left in the idle state if the transaction is to
resume. If this does not occur and the bus is left low for
more than 16µs (overdrive speed) or more than 120µs
(standard speed), one or more devices on the bus may
be reset. Note that the 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 and
adapters that are based on these driver chips.
Hardware Configuration
The 1-Wire bus has only a single line by definition; it is
important that each device on the bus be able to drive
it at the appropriate time. To facilitate this, each device
attached to the 1-Wire bus must have open-drain or
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 can
be boosted to 142kbps by activating the overdrive
mode. The DS1922L/DS1922T are not guaranteed to
be fully compliant to the iButton standard. Their maximum data rate in standard speed is 15.4kbps and
125kbps in overdrive speed. The value of the pullup
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 Configuration
36
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a
reset pulse transmitted by the bus master followed by
presence pulse(s) transmitted by the slave(s). The presence pulse lets the bus master know that the
DS1922L/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 can
issue 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 the
DS1922L/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 more
than one slave is present on the bus, a data collision
occurs 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 a
mismatch of the CRC.
Match ROM [55h]
The Match ROM command, followed by a 64-bit ROM
sequence, allows the bus master to address a specific
DS1922L/DS1922T on a multidrop bus. Only the
DS1922L/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 master
might not know the number of devices on the 1-Wire
bus or their registration numbers. By taking advantage
of the wired-AND property of the bus, the master can
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, the
bus 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, the
master knows that slave devices exist with both states
of 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 the
registration numbers of the remaining devices. Refer to
Application 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. After
each pass of the conditional search that successfully
determined the 64-bit ROM code for a specific device
on the multidrop bus, that particular device can be individually accessed as if a Match ROM had been issued,
since all other devices have dropped out of the search
process and 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 the
Conditional Search ROM command.
______________________________________________________________________________________
37
DS1922L/DS1922T
Initialization
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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 this
means 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 can
repeatedly 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 by
allowing 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
38
ROM command sets the DS1922L/DS1922T in the overdrive mode (OD = 1). All communication following this
command 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 that
exactly 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 the
next reset pulse of minimum 690µs duration. The
Overdrive-Match ROM command can be used with a
single or multiple devices on the bus.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
DS1922L/DS1922T
BUS MASTER Tx
RESET PULSE
FROM FIGURE 11b
FROM MEMORY/CONTROL FUNCTION
FLOWCHART (FIGURE 9)
OD
RESET PULSE?
N
OD = 0
Y
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 SEARCH
COMMAND?
N
Y
Y
Y
Y
RC = 0
RC = 0
RC = 0
RC = 0
N
N
TO FIGURE 11b
CONDITION
MET?
Y
DS1922 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?
N
N
BIT 1 MATCH?
Y
DS1922 Tx BIT 63
DS1922 Tx
CRC BYTE
BIT 0 MATCH?
Y
Y
Y
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 = 1
TO FIGURE 11b
FROM FIGURE 11b
TO MEMORY/CONTROL FUNCTION
FLOWCHART (FIGURE 9)
Figure 11a. ROM Functions Flowchart
______________________________________________________________________________________
39
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
TO FIGURE 11a
FROM FIGURE 11a
CCh
SKIP ROM
COMMAND?
N
Y
A5h
RESUME
COMMAND?
3Ch
OVERDRIVESKIP ROM?
N
Y
N
Y
RC = 1?
N
Y
RC = 0; OD = 1
RC = 0
69h
OVERDRIVEMATCH ROM?
RC = 0; OD = 1
N
Y
MASTER Tx
RESET?
Y
MASTER Tx BIT 0
N
(SEE NOTE)
MASTER Tx
RESET?
N
Y
BIT 0 MATCH?
N
OD = 0
Y
MASTER Tx BIT 1
(SEE NOTE)
BIT 1 MATCH?
N
OD = 0
Y
MASTER Tx BIT 63
(SEE NOTE)
BIT 63 MATCH?
N
OD = 0
Y
FROM FIGURE 11a
RC = 1
TO 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)
40
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
drive mode and tRSTL is no longer than 80µs, the device
remains in overdrive mode.
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 and
presence 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 get
from active to idle, the voltage needs to rise from
VILMAX past the threshold VTH. The time it takes for the
voltage to make this rise is seen in Figure 12 as “ε” and
its 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 the
falling edge, it must pull down the line for tRSTL + tF to
compensate for the edge. A tRSTL duration of 690µs or
longer exits the overdrive mode, returning the device to
standard 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 the
threshold 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, the
master 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 the
data 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 the
data 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
RESISTOR
MASTER
DS1922L/DS1922T
Figure 12. Initialization Procedure: Reset and Presence Pulse
______________________________________________________________________________________
41
DS1922L/DS1922T
1-Wire Signaling
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Master-to-Slave
For a write-one time slot, the voltage on the data line
must have crossed the VTH threshold before the write-one
low time tW1LMAX is expired. For a write-zero time slot,
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-Master
A 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 internal
timing generator determines when this pulldown ends
and the voltage starts rising again. When responding
with a 1, the DS1922L/DS1922T do not hold the data
line low at all, and the voltage starts rising as soon as
tRL is over.
The sum of tRL + δ (rise time) on one side and the internal timing generator of the DS1922L/DS1922T on the
other side define the master sampling window (tMSRMIN
to tMSRMAX) in which the master must perform a read
from the data line. For most reliable communication, tRL
should be as short as permissible and the master
should read close to but no later than tMSRMAX. After
reading from the data line, the master must wait until
tSLOT 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 the
physical 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 communication
42
line. Noise coupled onto the 1-Wire line from external
sources 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, as
a 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 to
noise and also reduces the magnitude of noise injected by the slave device itself.
The DS1922L/DS1922T’s 1-Wire front-end differs from
traditional slave devices in four characteristics:
1) The falling edge of the presence pulse has a controlled slew rate. This provides a better match to the
line impedance than a digitally switched transistor,
converting the high-frequency ringing known from
traditional devices into a smoother low-bandwidth
transition. The slew-rate control is specified by the
parameter 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 time
slot. This reduces the sensitivity to high-frequency
noise. This additional filtering does not apply at overdrive speed.
3) There is a hysteresis at the low-to-high switching
threshold VTH. If a negative glitch crosses VTH but
does not go below VTH - VHY, it is not recognized
(Figure 14, Case A). The hysteresis is effective at
any 1-Wire speed.
4) There is a time window specified by the rising edge
hold-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 the
improved 1-Wire front-end.
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
DS1922L/DS1922T
WRITE-ONE TIME SLOT
tW1L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
ε
tF
tSLOT
RESISTOR
MASTER
WRITE-ZERO TIME SLOT
tW0L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
ε
tF
tREC
tSLOT
RESISTOR
MASTER
READ-DATA TIME SLOT
tMSR
tRL
VPUP
VIHMASTER
VTH
MASTER
SAMPLING
WINDOW
VTL
VILMAX
0V
δ
tF
tREC
tSLOT
RESISTOR
MASTER
DS1922L/DS1922T
Figure 13. Read/Write Timing Diagrams
______________________________________________________________________________________
43
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
tREH
tREH
VPUP
VTH
VHY
CASE A
CASE B
CASE 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 OUTPUT
INPUT 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 the
DS1922L/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 when
reading 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 reading
from the scratchpad. In contrast to the 8-bit CRC, the
44
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 in
the command flowchart of Figure 9. The bus master
compares the CRC value read from the device to the
one it calculates from the data and decides whether to
continue with an operation or to reread the portion of
the data with the CRC error. With the initial pass
through 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-
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
shifting in the command code, the target addresses
TA1 and TA2, the E/S byte, and the scratchpad data
starting at the target address. The DS1922L/DS1922T
transmit this CRC only if the reading continues through
the 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
SYMBOL
DESCRIPTION
RST
1-Wire reset pulse generated by master.
PD
1-Wire presence pulse generated by slave.
Select
Command and data to satisfy the ROM function protocol.
WS
Command “Write Scratchpad.”
RS
Command “Read Scratchpad.”
CPS
Command “Copy Scratchpad with Password.”
RMC
Command “Read Memory with Password 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>
<32 Bytes>
<Data>
Transfer of 8 bytes that either represent a valid password or acceptable dummy data.
Transfer of 32 bytes.
Transfer of an undetermined amount of data.
FFh
Transmission of one FFh byte.
CRC-16
Transfer of an inverted CRC-16.
FF Loop
Indefinite loop where the master reads FF bytes.
AA Loop
Indefinite loop where the master reads AA bytes.
______________________________________________________________________________________
45
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 the
scratchpad 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 then
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Command-Specific 1-Wire Communication Protocol—Color Codes
Master-to-Slave
Slave-to-Master
1-Wire Communication Examples
Write Scratchpad, Reaching the End of the Scratchpad (Cannot Fail)
RST PD Select WS
TA
<Data to EOS>
CRC-16
FF Loop
Read Scratchpad (Cannot Fail)
RST PD Select RS
TA-E/S <Data to EOS>
CRC-16
FF Loop
Copy Scratchpad with Password (Success)
RST PD Select CPS TA-E/S
<PW/Dummy>
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-16
FF Loop
Loop
Read Memory with Password and CRC (Fail Password or Address)
RST PD Select RMC TA
<PW/Dummy>
FF Loop
Clear Memory with Password
RST PD Select CM
<PW/Dummy>
FFh
FF Loop
To verify success, read the General Status register at address 0215h. If MEMCLR is 1, the command was
executed successfully.
46
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
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.
Mission Example: Prepare
and Start a New Mission
Step 1: Clear the data of the previous mission.
Step 2: Write the setup data to register page 1.
Assumption: The previous mission has been ended by
using the Stop Mission command. Passwords are not
enabled. The device is a DS1922L.
Starting a mission requires three steps:
Step 3: Start the new mission.
Step 1: Clear the data of the previous mission.
MASTER MODE
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)
COMMENTS
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Clear Memory” command
Send dummy password
Send dummy byte
Reset pulse
Presence pulse
______________________________________________________________________________________
47
DS1922L/DS1922T
1-Wire Communication Examples (continued)
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
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
48
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 mission
that logs temperature using 8-bit format.
EXAMPLE VALUES
FUNCTION
15:30:00 hours
Time
1st of April in 2002
Date
Every 10 minutes (EHSS = 0)
Sample rate
0°C low
10°C high
Temperature 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
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
MASTER MODE
DATA (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>
Tx
<7 FFh Bytes>
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
Write 25 bytes of data to scratchpad
Write through the end of the scratchpad
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 the
Mission 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)
Reset pulse
Presence pulse
Send dummy password
Send dummy byte
Reset pulse
Presence pulse
______________________________________________________________________________________
49
DS1922L/DS1922T
With only a single device connected to the bus master,
the communication of step 2 looks like this:
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Software Correction Algorithm
for Temperature
The correction algorithm consists of two steps: preparation and execution. By means of the family code the
preparation 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 and
converted from binary to decimal °C format. Next,
three coefficients A, B, and C are computed. In the
execution step, the temperature reading as delivered
by the DS1922 is first converted from the lowbyte/high-byte format (TcL, TcH) to °C (Tc) and then
corrected to TCORR. Once step 1 is performed, the
three coefficients can be used repeatedly to correct
any temperature reading and temperature log of the
same device.
The accuracy of high-resolution temperature conversion results (forced conversion as well as temperature
logs) can be improved through a correction algorithm.
The data needed for this software correction is stored
in the calibration memory (memory page 18, duplicated
in page 19). This data consists of reference temperature (Tr) and conversion result (Tc) for two different temperatures. See the Temperature Conversion section for
the 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.
ADDRESS
DESIGNATOR
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)
50
______________________________________________________________________________________
Temperature Logger iButton with 8KB
Data-Log Memory
5.89mm
0.51mm
—
Err3 = -0.1483°C
Tc2 = -10.0625°C
Err1 = 0.0672°C
Tc3 = 24.5°C
—
A1
® 41
1-Wire®
W
W
B = -0.008741
16.25mm
000000FBC52B
YY
RESULTING CORRECTION
COEFFICIENTS
APPLICATION OF
CORRECTION
COEFFICIENTS TO SAMPLE
READING
t o n ®. c
ut
Thermochron®
0
Err2 = 0.0672°C
Tr3 = 24.6483°C
om
Tr2 = -10.1297°C
BRANDING
iB
Tr1 = 60°C
F5 SIZE
ERROR VALUES
F5
CONVERTED DATA FROM
CALIBRATION MEMORY
Pin Configuration
ZZZ D S1922L
#
17.35mm
IO
GND
—
A = 0.000175/°C
TC = 22.500°C
C = -0.039332°C
TCORR = 22.647°C
Note: The software correction requires floating-point arithmetic
(24 bit or better). Suitable math libraries for microcontrollers are
found on various websites and are included in cross compilers.
Package Information
For the latest package outline information and land patterns
(footprints), go to www.maxim-ic.com/packages. Note that a
“+”, “#”, or “-” in the package code indicates RoHS status only.
Package drawings may show a different suffix character, but
the drawing pertains to the package regardless of RoHS status.
PACKAGE
TYPE
PACKAGE
CODE
OUTLINE
NO.
LAND
PATTERN NO.
F5 iButton
IB#6CB
21-0266
—
Thermochron is a registered trademark of Maxim Integrated Products, Inc.
______________________________________________________________________________________
51
DS1922L/DS1922T
Numerical Correction Example
DS1922L/DS1922T
Temperature Logger iButton with 8KB
Data-Log Memory
Revision History
REVISION
NUMBER
7
REVISION
DATE
DESCRIPTION
PAGES
CHANGED
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 can
degrade the integrity of the seal over time, so for applications with significant
exposure to liquids, sprays, or other similar environments, it is recommended to place
the Thermochron in the DS9107 iButton capsule. The DS9107 provides a watertight
enclosure that has been rated to IP68 (See www.maximic.com/AN4126)
1, 4, 12
8
4/09
9
10/09
10
4/11
Created newer template-styled data sheet
Deleted the standard part numbers from the Ordering Information table
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
All
1
1, 3, 4, 13, 25
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
52 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2011 Maxim Integrated Products
Maxim is a registered trademark of Maxim Integrated Products, Inc.