DALLAS DS1922T

DS1922L, DS1922T
Temperature Logger iButton
With 8kB Datalog Memory
www.maxim-ic.com
GENERAL DESCRIPTION
SPECIAL FEATURES
®
§
The DS1922L/T 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 userdefined rate. A total of 8192 8-bit readings or 4096
16-bit readings taken at equidistant intervals ranging
from 1s to 273hrs can be stored. In addition to this,
there are 512 bytes of SRAM for storing applicationspecific information and 64 bytes for calibration data.
A mission to collect data can be programmed to
begin immediately, or after a user-defined delay or
after a temperature alarm. Access to the memory and
control functions can be password protected. The
DS1922L/T is configured and communicates with a
®
host computing device through the serial 1-Wire
protocol, which requires only a single data lead and a
ground return. Every DS1922L/T 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/T to be
mounted on almost any object, including containers,
pallets, and bags.
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APPLICATIONS
Temperature Logging in Cold Chain, Food Safety,
Bio Science, and Pharmaceutical and Medical
Products
High-Temperature Logging (Process Monitoring,
Industrial Temperature Monitoring)
Automatically Wakes up, Measures Temperature, and Stores Values in 8kB of Datalog
Memory in 8- or 16-Bit Format
Digital Thermometer Measures Temperature with
8-Bit (0.5°C) or 11-Bit (0.0625°C) Resolution
Accuracy Better than ±0.5°C from -10°C to
+65°C (DS1922L), ±0.5°C from +20°C to +75°C
(DS1922T) with Software Correction
Water resistant - 1 meter under water for 30 days
Sampling Rate from 1s up to 273hrs
Programmable Recording Start Delay After
Elapsed Time or Upon a Temperature Alarm Trip
Point
Programmable High and Low Trip Points for
Temperature Alarms
Quick Access to Alarmed Devices Through
1-Wire Conditional Search Function
512 Bytes of General-Purpose Plus 64 Bytes of
Calibration Memory
Two-Level Password Protection of All Memory
and Configuration Registers
Communicates to Host with a Single Digital
Signal at up to 15.4kbps at Standard Speed or
up to 125kbps in Overdrive Mode Using 1-Wire
Protocol
Operating Range: DS1922L: -40 to +85°C;
DS1922T: 0 to +125°C
PIN CONFIGURATION
5.89
0.51
ORDERING INFORMATION
PART
TEMP RANGE
DS1922L-F5
DS1922T-F5
-40°C to +85°C
0°C to +125°C
â
16.25
PACKAGE
F5 iButton
F5 iButton
A1
â
41
000000FBC52B
17.35
â
See page 11 for Common iButton Features and
Examples of Accessories.
1-Wire
Commands, Registers, and Modes are capitalized for
clarity.
IO
iButton and 1-Wire are registered trademarks of Dallas Semiconductor.
GND
ALL DIMENSIONS ARE SHOWN IN MILLIMETERS.
Note: Some revisions of this device may incorporate deviations from published specifications known as errata. Multiple revisions of any device
may be simultaneously available through various sales channels. For information about device errata, click here: www.maxim-ic.com/errata.
1 of 48
REV: 121003
DS1922L/DS1922T
ABSOLUTE MAXIMUM RATINGS
I/O Voltage to GND
I/O Sink Current
Operating Temperature Range (DS1922L)
Operating Temperature Range (DS1922T)
Junction Temperature
Storage Temperature Range (DS1922L)
Storage Temperature Range (DS1922T)
-0.3V, +6V
20mA
-40°C to +85°C
0°C to +125°C
+150°C
-40°C to +85°C*
0°C to +125°C*
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 the absolute maximum rating conditions for extended periods may affect device.
*Storage or operation above +50°C significantly reduces battery life.
ELECTRICAL CHARACTERISTICS
(VPUP = 3.0V to 5.25V, TA = -40°C to +85°C)
PARAMETER
I/O Pin General Data
1-Wire Pullup Resistance
Input Capacitance
Input Load Current
High-to-Low Switching
Threshold
Input Low Voltage
Low-to-High Switching
Threshold
Switching Hysteresis
Output Low Voltage
SYMBOL
RPUP
CIO
IL
CONDITIONS
MIN
TYP
MAX
UNITS
100
6
2.2
800
10
kW
pF
µA
3.2
V
0.3
V
0.7
3.4
V
0.09
N/A
0.4
V
V
(Notes 1, 2)
(Note 3)
I/O pin at VPUP
VTL
(Notes 4, 5)
VIL
(Notes 1, 6)
VTH
(Notes 4, 7)
0.4
VHY
VOL
(Note 8)
At 4mA (Note 9)
Standard speed, RPUP = 2.2kW
Overdrive speed, RPUP = 2.2kW
Recovery Time (Note 1)
tREC
Overdrive speed, directly prior to reset
pulse; RPUP = 2.2kW
Rising-Edge Hold-Off Time
tREH
(Note 10)
Standard speed
Timeslot Duration (Note 1)
tSLOT
Overdrive speed, VPUP > 4.5V
Overdrive speed (Note 11)
I/O Pin, 1-Wire Reset, Presence Detect Cycle
Standard speed, VPUP > 4.5V
Standard speed (Note 11)
Reset Low Time (Note 1)
tRSTL
Overdrive speed, VPUP > 4.5V
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence Detect High
Standard speed (Note 11)
tPDH
Time
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence Detect Fall Time
tFPD
Standard speed
(Note 12)
Overdrive speed
Standard speed, VPUP > 4.5V
Standard speed (Note 11)
Presence Detect Low
tPDL
Time
Overdrive speed, VPUP > 4.5V (Note 11)
Overdrive speed (Note 11)
Standard speed, VPUP > 4.5V
Presence Detect Sample
tMSP
Standard speed
Time (Note 1)
Overdrive speed
I/O Pin, 1-Wire Write
Standard speed
Write-0 Low Time (Note 1)
tW0L
Overdrive Speed, VPUP > 4.5V (Note 11)
Overdrive speed (Note 11)
Standard speed
Write-1 Low Time
tW1L
(Notes 1, 13)
Overdrive speed
2 of 48
5
2
µs
5
0.6
65
8
9.5
2.0
480
690
48
70
15
15
2
1.5
1.5
0.15
60
60
7
7
65
71.5
8
720
720
80
80
60
63.5
7
5
8
1
240
287
24
28
75
75
9
60
6
7.5
5
1
120
12
12
15 - e
1.95 - e
µs
µs
µs
µs
µs
µs
µs
µs
µs
DS1922L/DS1922T
I/O Pin, 1-Wire Read
Read Low Time
(Notes 1, 14)
Read Sample Time
(Notes 1, 14)
Real Time Clock
tRL
tMSR
Accuracy
Temperature Converter
Conversion Time
(Note 15)
Thermal Response Time
Constant (note 16)
Conv. Error Without
Software Correction (note
17)
Conv. Error With Software
Correction (Note 18)
Note 3:
Note 4:
Note 5:
Note 6:
Note 7:
Note 8:
Note 9:
Note 10:
Note 11:
Note 12:
Note 13:
Note 14:
Note 15:
Note 16:
Note 17:
Note 18:
5
1
tRL + d
tRL + d
15 - d
1.95 - d
15
1.95
-2
+2
min/
month
-40°C to +85°C
0°C to +125°C
-300
-600
+60
+60
PPM
8-bit mode
16-bit mode (11 bits)
30
240
75
600
ms
+25°C
Frequency Deviation
Note 1:
Note 2:
Standard speed
Overdrive speed
Standard speed
Overdrive speed
DF
tCONV
tRESP
iButton package
µs
µs
130
s
DJ
See Temperature Accuracy
Graphs
°C
DJ
See Temperature Accuracy
Graphs
°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 2.2kW resistor is used to pull up the data line, 2.5µs
after VPUP has been applied the parasite capacitance will not affect normal communications.
VTL, VTH are a function of the internal supply voltage.
Voltage below which, during a falling edge on I/O, a logic '0' is detected.
The voltage on I/O needs to be less or equal to VILMAX whenever the master drives the line low.
Voltage above which, during a rising edge on I/O, a logic '1' is detected.
After VTH is crossed during a rising edge on I/O, the voltage on I/O has to 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.
Highlighted numbers are NOT in compliance with the published iButton standards. See comparison table below.
Interval during the negative edge on I/O 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.
e represents the time required for the pullup circuitry to pull the voltage on I/O up from VIL to VTH.
d represents the time required for the pullup circuitry to pull the voltage on I/O up from VIL to the input high threshold of the bus
master.
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 of 2000.
http://www.cemagref.fr/English/index.htm Test Report No. E42.
Includes +0.1/-0.2oC calibration chamber measurement uncertainty.
Assumes using calibration memory with calibration equations for error compensation. Includes +0.1/-0.2oC calibration chamber
measurement uncertainty. Guaranteed by design.
STANDARD VALUES
DS1922L/T VALUES
PARAMETER
STANDARD SPEED
OVERDRIVE SPEED
STANDARD SPEED
OVERDRIVE SPEED
NAME
MIN
MAX
MIN
MAX
MIN
MAX
MIN
MAX
1)
tSLOT (incl. tREC)
61µs
(undef.)
7µs
(undef.)
65µs
(undef.)
9.5µs
(undef.)
tRSTL
480µs
(undef.)
48µs
80µs
690µs
720µs
70µs
80µs
tPDH
15µs
60µs
2µs
6µs
15µs
63.5µs
2µs
7µs
tPDL
60µs
240µs
8µs
24µs
60µs
287µs
7µs
28µs
tW0L
60µs
120µs
6µs
16µs
60µs
120µs
7.5µs
12µs
1)
Intentional change, longer recovery time requirement due to modified 1-Wire front end.
PHYSICAL SPECIFICATION
Size
Weight
Safety
See mechanical drawing
Ca. 3.3 grams
th
Meets UL#913 (4 Edit.); Intrinsically Safe Apparatus,
approval under Entity Concept for use in Class I,
Division 1, Group A, B, C, and D Locations (application
pending)
3 of 48
DS1922L/DS1922T
8-Bit Min. Product Lifetime (years)
DS1922L MINIMUM PRODUCT LIFETIME VS. TEMPERATURE, SLOW SAMPLING
Every Minute
Every 3 Min.
Every 10 Min.
Every 60 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
11-Bit Min. Product Lifetime
(years)
DS1922L: Temperature (°C)
Every Minute
Every 3 Min.
Every 10 Min.
Every 30 Min.
Every 60 Min.
Every 300 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
-40
-30
-20
-10
0
10
20
30
40
50
DS1922L: Temperature (°C)
4 of 48
60
70
80
DS1922L/DS1922T
8-Bit Min. Product Lifetime (days)
DS1922L MINIMUM PRODUCT LIFETIME VS. TEMPERATURE, FAST SAMPLING
Every Second
Every 3 Sec.
Every 10 Sec.
Every 30 Sec.
Every 60 Sec.
350
300
250
200
150
100
50
0
-40
-30
-20
-10
0
10
20
30
40
50
60
70
80
11-Bit M in. Product Lifetime
(days)
DS1922L: Temperature (°C)
Every Second
Every 3 Sec.
Every 30 Sec.
Every 60 Sec.
Every 10 Sec.
100
80
60
40
20
0
-40
-30
-20
-10
0
10
20
30
40
50
DS1922L: Temperature (°C)
5 of 48
60
70
80
DS1922L/DS1922T
8-Bit Min. Product Lifetime (years)
DS1922T MINIMUM PRODUCT LIFETIME VS. TEMPERATURE, SLOW SAMPLING
Every Minute
Every 3 Min.
Every 10 Min.
Every 60 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
100 110 120
11-Bit Min. Product Lifetime
(years)
DS1922T: Temperature (°C)
Every Minute
Every 3 Min.
Every 10 Min.
Every 30 Min.
Every 60 Min.
Every 300 Min.
No Samples
Osc. Off
10
9
8
7
6
5
4
3
2
1
0
0
10
20
30
40
50
60
70
80
90
DS1922T: Temperature (°C)
6 of 48
100 110 120
DS1922L/DS1922T
8-Bit Min. Product Lifetime (days)
DS1922T MINIMUM PRODUCT LIFETIME VS. TEMPERATURE, FAST SAMPLING
Every Second
Every 3 Sec.
Every 10 Sec.
Every 30 Sec.
Every 60 Sec.
350
300
250
200
150
100
50
0
0
10
20
30
40
50
60
70
80
90
100 110 120
11-Bit Min. Product Lifetime
(days)
DS1922T: Temperature (°C)
Every Second
Every 3 Sec.
Every 30 Sec.
Every 60 Sec.
Every 10 Sec.
100
80
60
40
20
0
0
10
20
30
40
50
60
70
80
90
DS1922T: Temperature (°C)
7 of 48
100 110 120
DS1922L/DS1922T
DS1922L MINIMUM PRODUCT LIFETIME VS. SAMPLE RATE
8-Bit Min. Product Lifetime (years)
-40°C
0°C
40°C
60°C
75°C
85°C
10
1
0.1
0.01
0.01
0.1
1
10
100
DS1922L: Minutes between Samples
11-Bit Min. Product Lifetime (years)
-40°C
0°C
40°C
60°C
75°C
85°C
10
1
0.1
0.01
0.001
0.01
0.1
1
10
DS1922L: Minutes between Samples
8 of 48
100
DS1922L/DS1922T
8-Bit Min. Product Lifetime (years)
DS1922T MINIMUM PRODUCT LIFETIME VS. SAMPLE RATE
0°C
40°C
60°C
95°C
110°C
125°C
75°C
85°C
10
1
0.1
0.01
0.01
0.1
1
10
100
DS1922T: Minutes between Samples
0°C
40°C
60°C
95°C
110°C
125°C
75°C
85°C
11-Bit Min. Product Lifetime
(years)
10
1
0.1
0.01
0.001
0.01
0.1
1
10
DS1922T: Minutes between Samples
9 of 48
100
DS1922L/DS1922T
DS1922L TEMPERATURE ACCURACY
Uncorrected Max Error
Uncorrected Min Error
SW Corrected Max Error
SW Corrected Min Error
2.0
DS1922L: Error (°C)
1.5
1.0
0.5
0.0
-0.5
-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
Uncorrected Max Error
Uncorrected Min Error
SW Corrected Max Error
SW Corrected Min Error
2.5
DS1922T: Error (°C)
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-2.5
0
10
20
30
40
50
60
70
80
90
Temperature (°C)
NOTE: The graphs are based on 11-bit data.
10 of 48
100 110 120
DS1922L/DS1922T
COMMON iButton FEATURES
§
§
§
§
§
§
§
§
§
§
Digital identification and information by momentary contact.
Unique factory-lasered 64-bit registration number assures 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 (4th Edit.); Intrinsically Safe Apparatus: approved under Entity Concept for use in Class I,
Division 1, Group A, B, C, and D Locations (application pending).
EXAMPLES OF ACCESSORIES
DS9096P
DS9101
DS9093RA
DS9093A
DS9092
Self-Stick Adhesive Pad
Multipurpose Clip
Mounting Lock Ring
Snap-In Fob
iButton Probe
APPLICATION
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. 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- or equipment-specific data files.
OVERVIEW
The block diagram in Figure 1 shows the relationships between the major control and memory sections of the
DS1922L/T. The device has six main data components: 1) 64-bit lasered ROM, 2) 256-bit scratchpad, 3) 512-byte
general-purpose SRAM, 4) two 256-bit register pages of timekeeping, control, status, and counter registers and
passwords, 5) 64 bytes of calibration memory, and 6) 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 1 shows the hierarchical structure of the 1-Wire protocol. The bus master must first provide one of the eight
ROM function commands: 1) Read ROM, 2) Match ROM, 3) Search ROM, 4) Conditional Search ROM, 5) Skip
ROM, 6) Overdrive-Skip ROM, 7) Overdrive-Match ROM or 8) Resume. Upon completion of an Overdrive ROM
command byte executed at standard speed, the device will enter Overdrive mode, where all subsequent
communication occurs at a higher speed. The protocol required for these ROM function commands is described in
Figure 11. After a ROM function command is successfully executed, the memory and control functions become
accessible and the master may provide any one of the nine 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.
11 of 48
DS1922L/DS1922T
Figure 1. DS1922L/T Block Diagram
1-Wire
Port
ROM
Function
Control
I/O
64-Bit
Lasered
ROM
Memory
Function
Control
3V Lithium
Parasite
Powered
Circuitry
256-Bit
Scratchpad
General-Purpose
SRAM
(512 Bytes)
Internal
Timekeeping &
Control Reg. &
Counters
32.768kHz
Oscillator
Thermal
Sense
Register Pages
(64 Bytes)
Calibration Memory
(64 Bytes)
ADC
Control
Logic
Datalog
Memory
8k Bytes
PARASITE POWER
The block diagram (Figure 1) shows the parasite-powered circuitry. This circuitry “steals” power whenever the I/O
input is high. I/O will provide sufficient power as long as the specified timing and voltage requirements are met. The
advantages of parasite power are two-fold: 1) by parasiting off this input, battery power is conserved; and 2) if the
battery is exhausted for any reason, the ROM may still be read.
64-BIT LASERED ROM
Each DS1922L/T 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 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
8
5
4
Figure 4. The polynomial is X + X + X + 1. Additional information about the Dallas 1-Wire Cyclic Redundancy
Check (CRC) is available in Application Note 27 and in the Book of DS19xx iButton Standards.
The shift register bits are initialized to 0. Then starting with the least significant bit of the family code, one bit at a
th
time is shifted in. After the 8 bit of the family code has been entered, then the serial number followed by the
temperature range code is entered. After the range code has been entered, the shift register contains the CRC
value. Shifting in the 8 bits of CRC returns the shift register to all 0s.
12 of 48
DS1922L/DS1922T
Figure 2. Hierachical Structure for 1-Wire Protocol
1-Wire net
BUS
Master
Other
Devices
DS1922L, DS1922T
Command
Level:
1-Wire ROM Function
Commands
Available
Commands:
Data Field
Affected:
Read ROM
Match ROM
Search ROM
Conditional Search 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
Skip ROM
Resume
Overdrive Skip
Overdrive Match
Write Scratchpad
Read Scratchpad
Copy Scratchpad w/PW
Read Memory w/PW &
w/CRC
Clear Memory w/PW
DS1922-Specific
Memory Function
Commands
Forced Conversion
Start Mission w/PW
Stop Mission w/PW
256-bit Scratchpad, Flags
256-bit Scratchpad
512 byte Data Memory, Registers,
Flags, Passwords
Memory, Registers, Passwords
Mission Time Stamp, Mission Samples
Counter, Start Delay, Alarm
Flags, Passwords
Memory addresses 020Ch to 020Dh
Flags, Timestamp, Memory addresses
020Ch to 020Dh (when logging)
Flags
Figure 3. 64-Bit Lasered ROM
MSB
LSB
8-Bit
CRC Code
MSB
8-Bit Family
Code (41h)
48-Bit Serial Number
LSB
MSB
LSB
MSB
LSB
Figure 4. 1-Wire CRC Generator
8
5
4
Polynomial = X + X + X + 1
st
nd
1
STAGE
X
0
rd
2
STAGE
X
1
th
3
STAGE
X
2
th
4
STAGE
X
3
th
5
STAGE
X
4
th
6
STAGE
X
5
th
7
STAGE
X
6
8
STAGE
X
7
INPUT DATA
13 of 48
X
8
DS1922L/DS1922T
MEMORY
The memory map of the DS1922L/T is shown in Figure 5. The 512 bytes general-purpose SRAM are located in
pages 0 through 15. The various registers to set-up and control the device fill page 16 and 17, called register pages
1 and 2 (details in Figure 6). Pages 18 and 19 provide storage space for calibration data. They can alternatively be
used as extension of the general-purpose memory. The "datalog" 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 page. 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
preceeding 31 bytes. Page 19 is an exact copy of the data in page 18. While the calibration memory can be
overwritten by the user, this is not recommended. See section Security by Password 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 datalog 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 Register and Transfer Status section for details.
Figure 5. DS1922L/T Memory Map
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
0220H to
023FH
0240H to
025FH
0260H to
027FH
0280H to
0FFFH
32-Byte Register Page 1
Page 16
32-Byte Register Page 2
Page 17
Calibration Memory Page 1 (R/W)
Page 18
Calibration Memory Page 2 (R/W)
Page 19
(Reserved For Future Extensions)
Pages 20 to 127
1000H to
2FFFH
Datalog Memory (Read-Only)
Pages 128
to 383
14 of 48
DS1922L/DS1922T
Figure 6. DS1922L/T Register Pages Map
ADDR
0200h
0201h
b7
0
0
b6
b5
10s
10min.
0202h
0
12/24
0203h
0204h
0205h
0206h
0207h
0208h
0209h
020Ah
020Bh
020Ch
020Dh
020Eh
020Fh
0210h
0211h
0212h
0213h
0214h
0215h
0216h
0217h
0218h
0219h
021Ah
0
CENT
0
0
021Bh
0
12/24
021Ch
021Dh
021Eh
021Fh
0220h
0221h
0222h
0223h
0224h
0225h
0226h
0227h
0228h
…
022Fh
0230h
…
0237h
0238h
…
023Fh
0
CENT
0
0
20hr
AM/PM
0
b4
b3
b2
b1
Single Seconds
Single Minutes
10hr
Single Hours
10 Date
10m.
Single Date
Single Months
Single Years
10yrs
b0
Low Byte
0
0
1
0
1
BOR
1
0
0
High Byte
Low Threshold
High Threshold
(no function with the DS1922L/T)
(no function with the DS1922L/T)
Low Byte
0
0
0
0
High Byte
(no function with the DS1922L/T)
(no function with the DS1922L/T)
0
0
0
0
0
ETHA
1
1
1
1
1
0
0
0
0
0
0
EHSS
1
SUTA
RO
(X)
TLFS
0
1
1
1
0
0
THF
1
0
WFTA MEMCLR
0
MIP
Low Byte
Center Byte
High Byte
10s
Single Seconds
10min.
Single Minutes
0
10hr
Single Hours
10 Date
10m.
Single Date
Single Months
Single Years
10yrs
Access*
RealTime
Clock
Registers
R/W; R
Sample
Rate
Temp.
Alarms
0
20hr
AM/PM
Function
0
ETLA
0
EOSC
ETL
TLF
0
R/W; R
R/W; R
(N/A)
R/W; R
Latest
Temp.
R; R
(N/A)
R; R
T.Alm.En.
(N/A)
RTC En.
Mis. Cntrl.
Alm. Stat.
Gen. Stat.
Start
Delay
Counter
R/W; R
R/W; R
R/W; R
R/W; R
R; R
R; R
Mission
Time
Stamp
(no function; reads 00h)
Low Byte
Center Byte
High Byte
Low Byte
Center Byte
High Byte
Configuration Code
EPW
First Byte
…
Eighth Byte
First Byte
…
Eighth Byte
(N/A)
Mission
Samples
Counter
Device
Samples
Counter
Flavor
PW. Cntrl.
Read
Access
Password
Full
Access
Password
(no function; all of these bytes read 00h)
(N/A)
R/W; R
R; R
R; R
R; R
R; R
R; R
R/W; R
W; --W; —
R; R
Note: The first entry in column ACCESS TYPE is valid between missions. The second entry shows the applicable
access type while a mission is in progress.
15 of 48
DS1922L/DS1922T
TIMEKEEPING AND CALENDAR
The real-time clock (RTC)/alarm and calendar information is accessed by reading/writing the appropriate bytes in
the register page, address 200h to 205h. 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 will always read 0 regardless of how they
are written. The number representation of the real-time clock registers is BCD format (binary-coded decimal).
Real-Time Clock and RTC Alarm Register Bitmap
ADDR
0200h
0201h
0202h
b7
0
0
0
b6
b5
10s
10min.
b4
b3
b2
b1
Single Seconds
Single Minutes
12/24
20hr
AM/PM
10hr
Single Hours
0203h
0204h
0205h
0
CENT
0
0
10 Date
0
10m.
Single Date
Single Months
Single Years
10yrs
b0
The RTC of the DS1922L/T can run in either 12-hour or 24-hour mode. Bit 6 of the Hours Register (address 202h)
is defined as the 12- or 24-hour mode select bit. When high, the 12-hour mode is selected. In the 12-hour mode, bit
5 is the AM/PM bit with logic 1 being PM. In the 24-hour mode, bit 5 is the 20-hour bit (20 to 23 hours). 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
th
a multiple of 4 the device will add a 29 of February. This will work 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 may be any value from 1 to
16383, coded as an unsigned 14-bit binary number. If EHSS = 1, the shortest time between logging events is 1
second and the longest (sample rate = 3FFFh) is 4.55 hours. If EHSS = 0, the shortest is 1 minute and the longest
time is 273.05 hours ( 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. A
sample rate of 0000h is not valid and must be avoided under all circumstances. This will cause the device
to enter into an unrecoverable state.
Sample Rate Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0206h
Sample Rate Low
0207h
0
0
Sample Rate High
During a mission, there is only read access to these registers. Bits cells marked "0" always read 0 and cannot be
written to 1.
TEMPERATURE CONVERSION
The DS1922L measures temperatures in the range of -40°C to +85°C. With the DS1922T the temperature range
begins at 0°C and ends at +125°C. Temperature values are represented as a 8- or 16-bit unsigned binary number
with a resolution of 0.5°C in the 8-bit mode and 0.0625°C in the 16-bit mode.
The higher temperature byte TRH is always valid. In the 16-bit mode only the three highest bits of the lower byte
TRL are valid. The five lower bits all read zero. TRL is undefined if the device is in 8-bit temperature mode. An outof-range temperature reading will be indicated as 00h or 0000h when too cold and FFh or FFE0h when too hot.
16 of 48
DS1922L/DS1922T
Latest Temperature Conversion Result Register Bitmap
ADDR
020Ch
020Dh
b7
T2
T10
b6
T1
T9
b5
T0
T8
b4
0
T7
b3
0
T6
b2
0
T5
b1
0
T4
b0
0
T3
TRL
TRH
With TRH and TRL representing the decimal equivalent of a temperature reading the temperature value is
calculated as
J(°C) = TRH/2 - 41 + TRL/512
J(°C) = TRH/2 - 41
(16 bit mode, TLFS = 1, see address 0213h)
(8 bit mode, TLFS = 0, see address 0213h)
This equation is valid for converting temperature readings stored in the datalog 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 equation above needs to be resolved to
TALM = 2 * J (°C) + 82
The "+82" applies to the DS1922L. For the DS1922T use "+2" instead of "+82".
Since the temperature alarm threshold is only one byte, the resolution or temperature increment is limited to 0.5°C.
The TALM value needs to 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 or 16 bit) only the most significant byte of a temperature conversion is used to determine
whether an alarm will be generated.
Temperature Conversion Examples
Mode
8-bit
8-bit
16-bit
16-bit
hex
54h
17h
54h
17h
TRH
decimal
84
23
84
23
hex
—
—
00h
60h
TRL
decimal
—
—
0
96
J(°C)
DS1922L
1.0
-29.5
1.000
-29.3125
J(°C)
DS1922T
41.0
10.5
41.000
10.6875
Temperature Alarm Threshold Examples
J(°C)
25.5
-10.0
TALM (DS1922L)
hex
decimal
85h
133
3Eh
62
J(°C)
65.5
30.0
TALM (DS1922T)
hex
decimal
85h
133
3Eh
62
TEMPERATURE SENSOR ALARM
The DS1922L/T has two Temperature Alarm Threshold Registers (address 0208h, 0209h) to store values, which
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.
Temperature Sensor Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0210h
0
0
0
0
0
0
ETHA
ETLA
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.
17 of 48
DS1922L/DS1922T
Register Details
BIT DESCRIPTION
BIT(S)
ETLA: Enable Temperature Low Alarm
b0
ETHA: Enable
Temperature High Alarm
b1
DEFINITION
This bit controls whether, during a mission, the temperature low alarm
flag (TLF) may 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 will not be generated.
This bit controls whether, during a mission, the temperature high alarm
flag (THF) may 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 will not be generated.
RTC CONTROL
To minimize the power consumption of a DS1922L/T, the RTC oscillator should be turned off when device is 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.
RTC Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0212h
0
0
0
0
0
0
EHSS
EOSC
During a mission, there is only read access to this register. Bits 2-7 have no function. They always read 0 and
cannot be written to 1.
Register Details
BIT DESCRIPTION
BIT(S)
EOSC: Enable Oscillator
b0
EHSS: Enable High
Speed Sample
b1
DEFINITION
This bit controls the crystal oscillator of the real-time clock. When set to
logic 1, the oscillator will start operation. When written to logic 0, the
oscillator will stop and the device is in a low-power data retention mode.
This bit must be 1 for normal operation. A temperature conversion
must not be attempted while the RTC oscillator is stopped. This
will cause the device to enter into an unrecoverable state.
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.
MISSION CONTROL
The DS1922L/T is set up for its operation by writing appropriate data to its 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)
is to be used and whether old data may be overwritten by new data, once the datalog memory is full. An additional
control bit can be set to tell the DS1922L/T to wait with logging data until a temperature alarm is encountered.
Mission Control Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0213h
1
1
SUTA
RO
(X)
TLFS
0
ETL
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 and DS1922T. Bit 1
must be set to 0. Under this condition the setting of bit 3 becomes a “don’t care”.
18 of 48
DS1922L/DS1922T
Register Details
BIT DESCRIPTION
BIT(S)
ETL: Enable Temperature
Logging
b0
TLFS: Temperature
Logging Format Selection
b2
RO: Rollover Control
b4
SUTA: Start Mission upon
Temperature Alarm
b5
DEFINITION
To set up the device for a temperature-logging mission, this bit must be
set to logic 1. The recorded temperature values will start at address
1000h.
This bit specifies the format used to store temperature readings in the
datalog memory. If this bit is 0, the data will be stored in 8-bit format. If
this bit is 1, the 16-bit format will be used (higher resolution). With 16-bit
format, the most-significant byte is stored at the lower address.
This bit controls whether, during a mission, the datalog memory is
overwritten with new data or whether data logging is stopped once the
datalog 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 will stop once the datalog
memory is full. However, the RTC will continue to run and the MIP bit
will remain set until the Stop Mission command is performed.
This bit specifies whether a mission begins immediately (includes
delayed start) or if a temperature alarm will be required to start the
mission. If this bit is 1, the device will perform an 8-bit temperature
conversion at the selected sample rate and begin with data logging only
if an alarming temperature (high alarm or low alarm) was found. The first
logged temperature will be one sample period after the alarm occurred.
ALARM STATUS
The fastest way to determine whether a programmed temperature threshold was exceeded during a mission is
through reading the Alarm Status Register. In a networked environment that contains multiple DS1922L/T iButtons
the devices that encountered an alarm can quickly be identified by means of the Conditional Search command (see
ROM Function Commands). The temperature alarm will only occur if enabled (see Temperature Sensor Alarm).
The BOR alarm is always enabled.
Alarm Status Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0214h
BOR
1
1
1
0
0
THF
TLF
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 and DS1922T. They always read 0. The alarm status bits are cleared simultaneously
when the Clear Memory function is invoked. See Memory and Control Functions for details.
Register Details
BIT DESCRIPTION
BIT(S)
TLF: Temperature Low
Alarm Flag
b0
THF: Temperature High
Alarm Flag
b1
BOR: Battery On Reset
Alarm
b7
DEFINITION
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.
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.
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 may still appear
functional, but it has lost its factory calibration. Any data found in the
datalog memory should be disregarded.
19 of 48
DS1922L/DS1922T
GENERAL STATUS
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/T is 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.
General Status Register Bitmap
ADDR
b7
b6
b5
b4
b3
b2
b1
0215h
1
1
0
WFTA MEMCLR
0
MIP
There is only read access to this register. Bits 0, 2, 5, 6, and 7 have no function.
b0
0
Register Details
BIT DESCRIPTION
BIT(S)
MIP: Mission In Progress
b1
MEMCLR: Memory
Cleared
b3
WFTA: Waiting for
Temperature Alarm
b4
DEFINITION
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 function commands Start Mission and
Stop Mission.
If this bit reads 1, the Mission Time Stamp, Mission Samples Counter,
as well as 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 will return to
0 as soon as a new mission is started by using the Start Mission
command. The memory has to be cleared in order for a mission to start.
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 will remain 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.
MISSION START DELAY
The content of the Mission Start Delay Counter tells how many minutes will have to expire from the time a mission
was started until the first measurement of the mission will take place (SUTA = 0) or until the device will start 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 16777215 minutes, equivalent to 11650 days or roughly 31 years. If the
start delay is non-zero and the SUTA bit is set to 1, first the delay has to expire before the device starts testing for
temperature alarms to begin logging data.
Mission Start Delay Counter
ADDR
b7
b6
b5
b4
b3
b2
0216h
Delay Low Byte
0217h
Delay Center Byte
0218h
Delay High Byte
During a mission, there is only read access to these registers.
b1
b0
For a typical mission, the Mission Start Delay is 0. If a mission is too long for a single DS1922L/T 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 datalog
memory is full.
20 of 48
DS1922L/DS1922T
MISSION TIME STAMP
The Mission Time Stamp indicates the date and time of the first temperature sample of the mission. There is only
read access to the Mission Time Stamp Register.
Mission Time Stamp Registers Bitmap
ADDR
0219h
021Ah
021Bh
b7
0
0
0
b6
b5
10s
10min.
b4
12/24
20hr
AM/PM
10hr
021Ch
0
0
021Dh
021Eh
CENT
0
b3
b2
b1
Single Seconds
Single Minutes
Single Hours
10 Date
0
b0
Single Date
10m.
Single Months
Single Years
10yrs
MISSION PROGRESS INDICATOR
Depending on settings in the Mission Control Register (address 0213h) the DS1922L/T will 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) provides the information to identify valid blocks of data that have been gathered during the current (MIP = 1)
or latest mission (MIP = 0). See Datalog Memory Usage for an illustration.
Mission Samples Counter Register Map
ADDR
b7
b6
b5
0220h
0221h
0222h
There is only read access to this register.
b4
b3
Low Byte
Center Byte
High Byte
b2
b1
b0
The number read from the Mission Samples Counter indicates how often the DS1922L/T 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.
OTHER INDICATORS
The Device Samples Counter is similar to the Mission Samples Counter. During a mission this counter increments
whenever the DS1922L/T wakes up to measure and log data and when the device is 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 functions like a gas gauge for the battery that powers the iButton.
Device Samples Counter Register Map
ADDR
b7
b6
b5
0223h
0224h
0225h
There is only read access to this register.
b4
b3
Low Byte
Center Byte
High Byte
b2
b1
b0
The Device Samples Counter is reset to zero when the iButton is assembled. The counter will increment a couple
of times during final test. The number format is 24-bit unsigned integer. The maximum number that can be
represented in this format is 16777215.
The Device Configuration Byte is used to allow the master to distinguish between the DS2422 chip, and different
versions of the DS1922 iButtons. The table below shows the codes assigned to the various devices.
21 of 48
DS1922L/DS1922T
Device Configuration Byte
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
0226h
0
0
0
0
0
0226h
0
1
0
0
0
0226h
0
1
1
0
0
There is only read access to this register.
0
0
0
0
0
0
0
0
0
DS2422
DS1922L
DS1922T
SECURITY BY PASSWORD
The DS1922L/T is 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 needs to
be transmitted right 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.
Password Control Register
ADDR
b7
b6
b5
b4
b3
0227h
EPW
During a mission, there is only read access to this register.
b2
b1
b0
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 will be 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 full-access password.
Before enabling password checking, passwords for read-only access as well as for full access (read/write/control)
need to 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.
Read Access Password Register
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
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
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
The Read Access Password needs to be transmitted exactly in the sequence RP0, RP1… RP62, RP63. This
password only applies to the function “Read Memory with CRC”. The DS1922L/T will deliver the requested data
only if the password transmitted by the master was correct or if password checking is not enabled.
Full Access Password Register
ADDR
b7
b6
b5
b4
b3
b2
b1
b0
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
There is only write access to this register. Attempting to read the password will report all zeros. The password
cannot be changed while a mission is in progress.
22 of 48
DS1922L/DS1922T
The Full Access Password needs to be transmitted exactly in the sequence FP0, FP1… FP62, FP63. It will affect
the functions “Read Memory with CRC”, “Copy Scratchpad”, “Clear Memory”, “Start Mission”, and “Stop Mission”.
The DS1922L/T executes 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 will remain in the scratchpad for public read access.
DATALOG MEMORY USAGE
Once setup for a mission, the DS1922L/T logs the temperature measurements at equidistant time points entry after
entry in its datalog memory. The datalog memory is able to store 8192 entries in 8-bit format or 4096 entries in 16bit 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 Time Stamp) 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/T will behave after the datalog 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 Time
Stamp will then allow reconstructing the time points of all values stored in the datalog memory. This gives the exact
history over time for the most recent measurements taken. Earlier measurements cannot be reconstructed.
Figure 7. Temperature Logging
ETL = 1
TLFS = 0
ETL = 1
TLFS = 1
1000h
8192
8-Bit Entries
Temperature
1000h
With 16-bit format,
the most-significant
byte is stored at the
lower address.
4096
16-Bit Entries
Temperature
2FFFh
2FFFh
23 of 48
DS1922L/DS1922T
MISSIONING
The typical task of the DS1922L/T iButton is recording temperature. Before the device can perform this function, it
needs to be set up properly. This procedure is called missioning.
First of all, DS1922L/T needs to have its real-time clock set to valid time and date. This reference time may 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 real-time clock oscillator must be running (EOSC = 1). The memory assigned
to store the Mission Time Stamp, Mission Samples 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
have to 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. How to convert a
temperature value into the binary code to be written to the threshold registers is described under Temperature
Conversion earlier in this document. In addition, the temperature alarm must be enabled for the low- and/or highthreshold. This makes the device respond to a Conditional Search command (see ROM Function Commands),
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). If the
estimated duration of a mission is 10 days (= 14400 minutes), for example, then the 8192-byte capacity of the
datalog memory would be sufficient to store a new 8-bit value every 1.8 minutes (110 seconds). If the datalog
memory of the DS1922L/T is 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 needs to 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 needs to be written to the Sample Rate
Register. The sample rate may be any value from 1 to 16383, coded as an unsigned 14-bit binary number. A
sample rate of all zeros is not valid and must be avoided under all circumstances. This will cause the
device to enter into an unrecoverable state. The fastest sample rate is one sample per second (EHSS = 1,
Sample Rate = 0001h) and the slowest is one sample every 273.05 hours (EHSS = 0, Sample Rate = 3FFFh). To
get one sample every 6 minutes, for example, the sample rate value needs to be set to 6 (EHSS = 0) or 360
decimal (equivalent to 0168h at EHSS = 1).
If there is a risk of unauthorized access to the DS1922L/T or manipulation of data, one should define passwords for
read access and full access. Before the passwords become effective, their use needs to be enabled. See Security
by Password for more details.
The last step to begin a mission is to issue the Start Mission command. As soon as it has received this command,
the DS1922L/T sets the MIP flag and clear the MEMCLR flag. With the immediate/delayed start mode (SUTA = 0),
after as many minutes as specified by the Mission Start Delay are over, the device will wake up, copy the current
date and time to the mission time stamp register, and log the first entry of the mission. This increments both the
Mission Samples Counter and Device Samples Counter. All subsequent log entries will be 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/T first waits until the start delay is over. Then the device wakes up in intervals as specified by the sample
rate and EHSS bit and measure the temperature. This will increment the Device Samples Counter only. Only after
an alarming temperature is encountered will the DS1922L/T set the mission time stamp. The first sample of the
mission is logged one sample period after the temperature alarm occurred. From then on, both the Mission
Samples Counter and Device Samples Counter 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 memory of the DS1922L/T can be read at any time, e. g., to watch the progress of a mission.
Attempts to read the passwords will read 00h bytes instead of the data that is stored in the password registers.
24 of 48
DS1922L/DS1922T
ADDRESS REGISTERS AND TRANSFER STATUS
Because of the serial data transfer, the DS1922L/T employs 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 are written or from
which data are 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/T requires that the Ending Offset is always 1Fh
for a Copy Scratchpad 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, then the scratchpad
stores incoming data beginning at the byte offset 1Ch and will be full after only 4 bytes. The corresponding ending
offset in this example is 1Fh. For best economy of speed and efficiency, the target address for writing should point
to the beginning of a page, i.e., the byte offset will be 0. Thus the full 32-byte capacity of the scratchpad is
available, resulting also in the ending offset of 1Fh. The ending offset together with the PF is mainly a means to
support the master checking the data integrity after a Write command. The highest valued bit of the E/S Register,
called AA or Authorization Accepted, indicates that a valid copy command for the scratchpad has been received
and executed. Writing data to the scratchpad clears this flag.
Figure 8. Address Registers
Bit #
7
6
5
4
3
2
1
0
Target Address (TA1)
T7
T6
T5
T4
T3
T2
T1
T0
Target Address (TA2)
T15
T14
T13
T12
T11
T10
T9
T8
Ending Address with
Data Status (E/S)
(Read Only)
AA
0
PF
E4
E3
E2
E1
E0
WRITING WITH VERIFICATION
To write data to the DS1922L/T, the scratchpad has to be used as intermediate storage. First the master issues the
Write Scratchpad command to specify the desired target address, followed by the data to be written to the
scratchpad. In the next step, the master sends the Read Scratchpad command to read the scratchpad and to verify
data integrity. As preamble to the scratchpad data, the DS1922L/T sends the requested target address TA1 and
TA2 and the contents of the E/S Register. If the PF flag is set, data did not arrive correctly in the scratchpad. The
master does not need to continue reading; it can start a new trial to write data to the scratchpad. Similarly, a set AA
flag indicates that the Write command was not recognized by the device. If everything went correctly, both flags are
cleared and the ending offset indicates the address of the last byte written to the scratchpad. Now the master can
continue verifying every data bit. After the master has verified the data, it has to send the Copy Scratchpad
command. This command must be followed exactly by the data of the three address registers TA1, TA2, and E/S
as the master has read them verifying the scratchpad. As soon as the DS1922L/T has received these bytes, it
copies the data to the requested location beginning at the target address.
25 of 48
DS1922L/DS1922T
MEMORY- AND CONTROL-FUNCTION COMMANDS
The Memory/Control Function Flow Chart (Figure 9) describes the protocols necessary for accessing the memory
and the special function registers of the DS1922L/T. An example on how to use these and other functions to set up
the DS1922L/T for a mission is included at the end of this document, preceding the Electrical Characteristics
section. The communication between master and DS1922L/T takes place either at regular speed (default, OD = 0)
or at Overdrive Speed (OD = 1). If not explicitly set into the Overdrive mode the DS1922L/T assumes regular
speed. Internal memory access during a mission has priority over external access through the 1-Wire interface.
This affects several of the commands described below. See section Memory Access Conflicts for details and
remedies.
WRITE SCRATCHPAD COMMAND [0FH]
After issuing the Write Scratchpad command, the master must first provide the 2-byte target address, followed by
the data to be written to the scratchpad. The data is written to the scratchpad starting at the byte offset (T4:T0).
The master has to 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/T (see Figure 15)
calculates a CRC of the entire data stream, starting at the command code and ending at the last data byte sent by
the master. This CRC is generated using the CRC16 polynomial by first clearing the CRC generator and then
shifting in the command code (0Fh) of the Write Scratchpad command, the target addresses TA1 and TA2 as
supplied by the master and all the data bytes. If the ending offset is 11111b, the master may send 16 read time
slots and receive the inverted CRC16 generated by the DS1922L/T.
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 will fail during a mission.
READ SCRATCHPAD COMMAND [AAH]
This command is used to verify scratchpad data and target address. After issuing the Read Scratchpad command,
the master begins reading. The first 2 bytes will be the target address. The next byte is the ending offset/data
status byte (E/S) followed by the scratchpad data beginning at the byte offset (T4:T0), as shown in Figure 8. The
master may continue reading data until the end of the scratchpad after which it receives an inverted CRC16 of the
command code, Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the target
address. After the CRC is read, the bus master reads logical 1s from the DS1922L/T 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 will fail. The device will stop communicating and will wait for a reset pulse. If the password
was correct or if passwords were not enabled, the device will test the 3-byte authorization code. If the authorization
code pattern matches, the AA (Authorization Accepted) flag will be set and the copy will begin. A pattern of
alternating 1s and 0s will be transmitted after the data has been copied until the master issues a reset pulse. While
the copy is in progress any attempt to reset the part will be ignored. Copy typically takes 2µs per byte.
The data to be copied is determined by the three address registers. The scratchpad data from the beginning offset
through the ending offset will be copied, starting at the target address. The AA flag will remain 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 progress, write attempts
to the register pages are not successful. The AA bit (Authorization Accepted) remaining at 0 indicates this.
26 of 48
DS1922L/DS1922T
Figure 9-1. Memory/Control Function Flow Chart
From ROM Functions
Flow Chart (Figure 11)
Master TX Memory or
Control Fkt. Command
0FH
Write
Scratchpad
AAH
Read
Scratchpad
N
Y
Y
Master TX
TA1 (T7:T0)
Master RX
TA1 (T7:T0)
Master TX
TA2 (T15:T8)
Master RX
TA2 (T15:T8)
DS1922 sets Scratchpad Offset = (T4:T0)
and Clears (PF, AA)
Master RX Ending
Offset with Data
Status (E/S)
DS1922 sets (E4:E0)
= Scratchpad Offset
DS1922 Increments Scratchpad Offset
N
Y
Master RX Data Byte
from Scratchpad Offset
Y
Master
TX Reset?
DS1922 Increments Scratchpad Offset
N
Scratchpad Offset =
11111b?
Partial
Byte Written?
Y
To Figure 9
2nd Part
DS1922 sets Scratchpad Offset = (T4:T0)
Master TX Data Byte
to Scratchpad Offset
Master
TX Reset?
N
Master
TX Reset?
N
Y
N
Y
N
Scratchpad Offset =
11111b?
Y
Master RX CRC16 of
Command, Address Data,
E/S Byte, and Data Starting
at the Target Address
PF = 1
N
Master RX CRC16 of
Command, Address Data
Y
Y
Master
TX Reset?
N
Master
TX Reset?
Master RX "1"s
N
Master RX "1"s
To ROM Functions
Flow Chart (Figure 11)
27 of 48
From Figure 9
2nd Part
DS1922L/DS1922T
Figure 9-2. Memory/Control Function Flow Chart
From Figure 9
1st Part
99H
Copy Scrpd.
[w/PW]
To Figure 9
3rd Part
N
Y
Master TX
TA1 (T7:T0), TA2 (T15:T8)
Authorization
Code
Master TX
E/S Byte
Master TX
64-Bits [Password]
N
Password
Accepted?
Y
N
Authorization
Code Match?
Y
AA = 1
DS1922 Copies Scratchpad
Data to Memory
Master
RX "1"s
Master
RX "1"s
N
Copying
Finished
Master
TX Reset?
Y
DS1922 TX "0"
N
Y
Y
Master
TX Reset?
N
DS1922 TX "1"
To Figure 9
1st Part
N
Master
TX Reset?
Y
28 of 48
From Figure 9
3rd Part
DS1922L/DS1922T
Figure 9-3. Memory/Control Function Flow Chart
From Figure 9
2nd Part
69H
Read Mem.
[w/PW]&CRC
To Figure 9
4th Part
N
Y
Master TX
TA1 (T7:T0), TA2 (T15:T8)
Master TX
64-Bits [Password]
Decision made
by DS1922
N
Password
Accepted?
Y
DS1922 sets Memory
Address = (T15:T0)
Decision made
by Master
Master RX Data Byte
from Memory Address
Y
DS1922 Increments Address
Counter
Master
TX Reset?
N
End of Page?
N
Y
Master RX CRC16 of
Command, Address, Data
(1st Pass); CRC16 of Data
(Subsequent Passes)
Master TX
Reset
N
CRC OK?
Y
End of
Memory?
N
Y
Master RX "1"s
To Figure 9
2nd Part
Master TX
Reset?
Y
29 of 48
N
From Figure 9
4th Part
DS1922L/DS1922T
Figure 9-4. Memory/Control Function Flow Chart
From Figure 9
3rd Part
96H
Clear Mem.
[w/PW]
55H
Forced
Conversion?
N
Y
To Figure 9
5th Part
Y
Master TX
FFh dummy byte
Master TX
64-Bits [Password]
Master TX
FFh dummy byte
Mission in
Progress?
Y
N
N
Password
Accepted?
N
DS1922 Performs a
Temp. Conversion
Y
DS1922 copies Result
to Address 020C/Dh
Y
Mission in
Progress?
N
DS1922 clears Mission
Time Stamp, Mission
Samples Counter,
Alarm Flags
N
DS1922 sets
MEMCLR = 1
Master
TX Reset?
Y
N
Master
TX Reset?
Y
From Figure 9
5th Part
To Figure 9
3rd Part
30 of 48
DS1922L/DS1922T
Figure 9-5. Memory/Control Function Flow Chart
From Figure 9
4th Part
CCH
Start Mission
[w/PW]
33H
Stop Mission
[w/PW]
N
Mission Start
Delay Process
Y
Master TX
64-Bits [Password]
N
Y
Master TX
64-Bits [Password]
Y
Start Delay
Counter = 0?
Master TX
FFh dummy byte
Master TX
FFh dummy byte
N
N
Password
Accepted?
DS1922 Waits for 1 Minute
DS1922 decrements
Start Delay Counter
Y
Y
Mission in
Progress?
MEMCLR
= 1?
DS1922 Waits One
Sample Period
Y
DS1922 sets
MIP = 1
MEMCLR = 0
DS1922 Initiates
Mission Start Delay
Process
Y
MIP = 0?
N
N
Y
DS1922 sets WFTA=0
DS1922 Waits One
Sample Period
DS1922 copies RTC
Data to Mission Time
Stamp Register
N
To Figure 9
4th Part
Master
TX Reset?
Y
DS1922 Starts Logging
Taking First Sample
End Of Process
31 of 48
DS1922 sets
MIP = 0
WFTA = 0
Master
TX Reset?
DS1922 Performs 8-bit
Temp. Conversion
Temp.
Alarm?
N
Y
DS1922 Sets WFTA=1
N
Mission in
Progress?
Y
N
N
Y
N
SUTA = 1?
Password
Accepted?
Y
N
DS1922L/DS1922T
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 will fail. The device will stop communicating and will wait for a reset
pulse. If the password was correct or if passwords were not enabled, the master reads data from the DS1922L/T
beginning from the starting address and continuing until the end of a 32-byte page is reached. At that point the bus
master will send 16 additional read data time slots and receive the inverted 16-bit CRC. With subsequent read data
time slots the master will receive data starting at the beginning of the next memory page followed again by the
CRC for that page. This sequence will continue until the bus master resets the device. When trying to read the
passwords or memory areas that are marked as "reserved", the DS1922L/T will 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 2 address bytes and the contents of the data
memory. Subsequent passes through the Read Memory with CRC flow will generate a 16-bit CRC that is the result
of clearing the CRC generator and then shifting in the contents of the data memory page. After the 16-bit CRC of
the last page is read, the bus master will receive logical 1s from the DS1922L/T until a reset pulse is issued. The
Read Memory with CRC command sequence can be ended at any point by issuing a reset pulse.
CLEAR MEMORY WITH PASSWORD [96H]
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 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 in progress, the Clear Memory with Password command will fail.
The device will stop communicating and will wait for a reset pulse. If the password was correct or if passwords
were not enabled, the device will clear the Mission Time Stamp, Mission Samples Counter, and all alarm flags of
the Alarm Status Register. After these cells are cleared, the MEMCLR bit of the General Status Register will read 1
to indicate the successful execution of the Clear Memory with Password command. Clearing of the datalog memory
is not necessary because the Mission Samples Counter indicates how many entries in the datalog memory are
valid.
FORCED CONVERSION [55H]
The Forced Conversion command can be used to measure the temperature without starting a mission. After the
command code the master has to send one FFh byte to get the conversion started. The conversion result is found
as 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 600 ms to complete. During this time memory
access through the 1-Wire interface is blocked. The device will behave the same way as during a mission when the
sampling interferes with a memory/control function command. See section Memory Access Conflicts for details. A
forced conversion must not be attempted while the RTC oscillator is stopped. This will cause the device to
enter into an unrecoverable state.
START MISSION WITH PASSWORD [CCH]
The DS1922L/T uses 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 a 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 will fail. The device will stop communicating and will wait for a reset pulse. If the
password was correct or if passwords were not enabled, the device will start a mission. The sampling and data
logging will begin as soon as the mission start delay is over (SUTA = 0) and, if SUTA = 1, one sample period after
a temperature alarm was encountered. While the device is waiting for a temperature alarm to occur, the WFTA flag
in the general status register will read 1. During a mission there is only read access to the Register Pages.
32 of 48
DS1922L/DS1922T
STOP MISSION WITH PASSWORD [33H]
The DS1922L/T uses 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 will fail. The device will stop
communicating and will wait for a reset pulse. If the password was correct or if passwords were not enabled, the
device will clear the MIP bit in the General Status Register and restore 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.
MEMORY ACCESS CONFLICTS
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) will not perform
properly when internal and "external" activities interfere with each other. Not affected are the commands Start
Mission, Forced Conversion and Clear Memory, because they are not applicable while a mission is in progress or
while the device is waiting for a temperature alarm. The table below explains how the remaining five commands are
affected by internal activity, how to detect this interference and how to work around it.
INDICATION OF
INTERFERENCE
COMMAND
Write Scratchpad
Read Scratchpad
Copy Scratchpad
Read Memory with
CRC
Stop Mission
REMEDY
The CRC16 at the end of the
command flow reads FFFFh.
The data read changes to FFh
bytes or all bytes received are
FFh, including the CRC at the
end of the command flow.
The device behaves as if
Authorization Code or password was not valid or as if the
copy function would not end.
The data read changes to all
FFh bytes or all bytes received
are FFh, including the CRC at
the end of the command flow,
despite a valid password.
The general Status register at
address 215h reads FFh or the
MIP bit is 1 while bits 0, 2, and
5 are 0.
Wait 0.5 s, 1-Wire reset, address the device, repeat
Write Scratchpad with the same data and check the
validity of the CRC16 at the end of the command flow.
Alternatively, use Read Scratchpad to verify data
integrity.
Wait 0.5s, 1-Wire reset, address the device, repeat
Read Scratchpad and check the validity of the CRC16
at the end of the command flow.
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.
Wait 0.5s, 1-Wire reset, address the device, repeat
Read Memory with CRC and check the validity of the
CRC16 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
215h and check the MIP-bit. If the MIP-bit is 0, Stop
Mission was successful.
The interference is more likely to be seen with a high sample rate (1 sample every second) and with high-resolution
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.
1-Wire BUS SYSTEM
The 1-Wire bus is a system, which has a single bus master and one or more slaves. In all instances the DS1922L/T
is a slave device. 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. For a more detailed protocol description, refer to Chapter 4 of the
Book of DS19xx iButton Standards.
33 of 48
DS1922L/DS1922T
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 tri-state
outputs. The 1-Wire port of the DS1922L/T 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/T is not guaranteed to be fully compliant to the iButton standard. Its maximum data rate in standard
speed mode is 15.4kbps and 125kbps in Overdrive. The value of the pullup resistor primarily depends on the
network size and load conditions. The DS1922L/T requires a pullup resistor of maximum 2.2kW at any speed.
The idle state for the 1-Wire bus is high. If for any reason a transaction needs to be suspended, the bus MUST be
left in the idle state if the transaction is 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/T does not quite meet the full 16µs maximum low time of the normal 1-Wire bus Overdrive timing.
With the DS1922L/T the bus must be left low for no longer than 12µs at Overdrive to ensure that no DS1922L/T on
the 1-Wire bus performs a reset. The DS1922L/T communicates properly when used in conjunction with a
DS2480B or DS2490 1-Wire driver and adapters that are based on these driver chips.
Figure 10. Hardware Configuration
BUS MASTER
VPUP
DS1922L/T 1-Wire PORT
RPUP
RX
DATA
TX
RX = RECEIVE
Open-Drain
Port Pin
RX
TX
5µA
Typ.
TX = TRANSMIT
100W
MOSFET
TRANSACTION SEQUENCE
The protocol for accessing the DS1922L/T through the 1-Wire port is as follows:
§
§
§
§
Initialization
ROM Function Command
Memory/Control Function Command
Transaction/Data
INITIALIZATION
All transactions on the 1-Wire bus begin with an initialization sequence. The initialization sequence consists of a
reset pulse transmitted by the bus master followed by presence pulse(s) transmitted by the slave(s). The presence
pulse lets the bus master know that the DS1922L/T is on the bus and is ready to operate. For more details, see the
1-Wire Signaling section.
34 of 48
DS1922L/DS1922T
1-Wire ROM FUNCTION COMMANDS
Once the bus master has detected a presence, it can issue one of the eight ROM function commands that the
DS1922L/T supports. All ROM function commands are 8 bits long. A list of these commands follows (refer to
flowchart in Figure 11).
READ ROM [33H]
This command allows the bus master to read the DS1922L/T’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 wiredAND 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/T on a multidrop bus. Only the DS1922L/T 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 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 romcode
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 App Note 187: 1-Wire Search Algorithm for a
detailed discussion, including an example.
CONDITIONAL SEARCH [ECH]
The Conditional Search ROM command operates similarly to the Search ROM command except that only those
devices, which fulfill certain conditions, participates 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 will
have dropped out of the search process and will be waiting for a reset pulse.
The DS1922L/T will respond to the conditional search if one of the three alarm flags of the Alarm Status Register
(address 0214h) reads 1. The temperature alarm will only occur if enabled (see Temperature Sensor Alarm). The
BOR alarm is always enabled. The first alarm that occurs will make the device respond to the Conditional Search
command.
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. If more than one slave is present on the bus and, for example, a
Read command is issued following the Skip ROM command, data collision will occur on the bus as multiple slaves
transmit simultaneously (open-drain pulldowns will produce a wired-AND result).
35 of 48
DS1922L/DS1922T
RESUME COMMAND [A5h]
The DS1922L/T needs to be accessed several times before a mission will start. In a multidrop environment this
means that the 64-bit ROM code after a Match ROM command has to be repeated for every access. To maximize
the data throughput in a multidrop environment, the Resume function was implemented. This function 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 function.
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 ROM sets
the DS1922L/T in the Overdrive mode (OD = 1). All communication following this command has to 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 has to 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 wired-AND 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/T on a multidrop bus and to simultaneously set it in Overdrive mode.
Only the DS1922L/T that exactly matches the 64-bit ROM sequence responds to the subsequent memory/control
function command. Slaves already in Overdrive mode from a previous Overdrive Skip or successful Overdrive
Match command remain in Overdrive mode. All overdrive-capable slaves will 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.
36 of 48
DS1922L/DS1922T
Figure 11-1. ROM Funtions Flow Chart
Bus Master TX
Reset Pulse
From Memory Functions
Flow Chart (Figure 9)
From Figure 11, 2
OD
Reset Pulse?
N
nd
Part
OD = 0
Y
Bus Master TX ROM
Function Command
33h
Read ROM
Command?
Y
RC = 0
DS1922 TX
Presence Pulse
N
55h
Match ROM
Command?
F0h
Search ROM
Command?
N
Y
To Figure 11
nd
2 Part
ECh
Cond. Search
Command?
N
Y
RC = 0
N
Y
RC = 0
RC = 0
N
Condition Met?
Y
DS1922 TX
Family Code
(1 Byte)
Master TX Bit 0
N
Bit 0
Match?
N
N
Bit 0
Match?
N
N
Bit 1
Match?
Y
Y
DS1922 TX Bit 63
DS1922 TX Bit 63
Master TX Bit 63
DS1922 TX Bit 63
DS1922 TX Bit 63
Master TX Bit 63
Master TX Bit 63
N
Bit 63
Match?
DS1922 TX Bit 1
DS1922 TX Bit 1
Master TX Bit 1
N
Bit 1
Match?
Y
DS1922 TX
CRC Byte
Y
DS1922 TX Bit 1
DS1922 TX Bit 1
Master TX Bit 1
Master TX Bit 1
Bit 1
Match?
Bit 0
Match?
Y
Y
DS1922 TX
Serial Number
(6 Bytes)
DS1922 TX Bit 0
DS1922 TX Bit 0
Master TX Bit 0
DS1922 TX Bit 0
DS1922 TX Bit 0
Master TX Bit 0
N
N
Bit 63
Match?
Y
Bit 63
Match?
Y
RC = 1
RC = 1
To Memory Functions
Flow Chart (Figure 9)
37 of 48
Y
RC = 1
To Figure 11
nd
2 Part
From Figure 11
nd
2 Part
DS1922L/DS1922T
Figure 11-2. ROM Functions Flow Chart
st
To Figure 11, 1 Part
From Figure 11
st
1 Part
CCh
Skip ROM
Command?
Y
N
A5h
Resume
Command?
3Ch
Overdrive
Skip ROM?
N
Y
N
Y
RC = 0
Y
RC = 0 ; OD = 1
RC = 1 ?
69h
N
Overdrive Match
ROM?
RC = 0 ; OD = 1
N
Master TX Bit 0
Y
Master
TX Reset ?
Y
N
Bit 0
Match?
Y
N
Master TX Bit 1
Master
TX Reset ?
Y
N
Bit 1
Match?
Y
N
Master TX Bit 63
N
Bit 63
Match?
Y
From Figure 11
st
1 Part
RC = 1
To Figure 11
st
1 Part
38 of 48
DS1922L/DS1922T
1-Wire SIGNALING
The DS1922L/T requires strict protocols to ensure data integrity. The protocol consists of four types of signaling on
one line: reset sequence with reset pulse and presence pulse, write-zero, write-one, and read-data. Except for the
presence pulse, the bus master initiates all these signals. The DS1922L/T can communicate at two different
speeds, standard speed and Overdrive speed. If not explicitly set into the Overdrive mode, the DS1922L/T will
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 'e' and its duration depends on the pullup resistor (RPUP) used and the
capacitance of the 1-Wire network attached. The voltage VILMAX is relevant for the DS1922L/T when determining a
logical level, not triggering any events.
The initialization sequence required to begin any communication with the DS1922L/T is shown in Figure 12. A reset
pulse followed by a presence pulse indicates the DS1922L/T is ready to receive data, given the correct ROM and
memory function command. If the bus master uses slew-rate control on the falling edge, it must pull down the line
for tRSTL + tF to compensate for the edge. A tRSTL duration of 690µs or longer will exit the Overdrive mode returning
the device to standard speed. If the DS1922L/T is in Overdrive mode and tRSTL is no longer than 80µs the device
will remain in Overdrive mode.
Figure 12. Initialization Procedure “Reset and Presence Pulses”
MASTER TX “RESET PULSE” MASTER RX “PRESENCE PULSE”
VTL
VILMAX
0V
tMSP
e
VPUP
VIHMASTER
VTH
tF
tRSTL
RESISTOR
tPDH
MASTER
tPDL
tRSTH
tREC
DS1922L/T
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 case of a DS2480B driver, by active circuitry. When the threshold VTH is crossed,
the DS1922L/T waits for tPDH and then transmits 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, tPDLMAX, and tRECMIN. Immediately after tRSTH is expired, the
DS1922L/T is ready for data communication. In a mixed population network tRSTH 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/T takes place in time slots, which 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/T starts its 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.
39 of 48
DS1922L/DS1922T
MASTER-TO-SLAVE
For a write-one time slot, the voltage on the data line must have crossed the VTH threshold before the 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/T needs a recovery
time tREC before it is ready for the next time slot.
Figure 13. Read/Write Timing Diagram
Write-One Time Slot
tW1L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
e
tSLOT
RESISTOR
MASTER
Write-Zero Time Slot
tW0L
VPUP
VIHMASTER
VTH
VTL
VILMAX
0V
tF
tSLOT
RESISTOR
tREC
MASTER
Read-Data Time Slot
tMSR
tRL
VPUP
VIHMASTER
VTH
Master
Sampling
Window
VTL
VILMAX
0V
tF
d
RESISTOR
tREC
tSLOT
MASTER
DS1922L/T
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/T starts pulling the
data line low; its internal timing generator determines when this pulldown ends and the voltage starts rising again.
When responding with a 1, the DS1922L/T does not hold the data line low at all, and the voltage starts rising as
soon as tRL is over.
40 of 48
DS1922L/DS1922T
The sum of tRL + d (rise rime) on one side and the internal timing generator of the DS1922L/T 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/T to get ready for the next time slot.
IMPROVED NETWORK BEHAVIOR
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 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/T uses a new 1-Wire front end, which makes it less sensitive to noise and also
reduces the magnitude of noise injected by the slave device itself.
The 1-Wire front end of the DS1922L/T 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 low-pass 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 doesn’t go
below VTH - VHY, it will not be 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 will be ignored,
even if they extend below VTH - VHY threshold (Figure 14, Case B, tGL < tREH). Deep voltage droops or glitches
that appear late after crossing the VTH threshold and extend beyond the tREH window cannot be filtered out and
will be taken as beginning of a new time slot (Figure 14, Case C, tGL ³ tREH).
Only devices which have the parameters tFPD, VHY and tREH specified in their electrical characteristics use the
improved 1-Wire front end.
Figure 14. Noise Suppression Scheme
tREH
VPUP
tREH
VTH
VHY
Case A
0V
Case B
tGL
Case C
tGL
41 of 48
DS1922L/DS1922T
CRC GENERATION
With the DS1922L/T there are two different types of CRCs (Cyclic Redundancy Checks). 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/T to determine if the ROM
8
5
4
data has been received error-free. The equivalent polynomial function of this CRC is: X + X + X + 1. This 8-bit
CRC is received in the true (non-inverted) form. It is computed at the factory and lasered into the ROM.
16
15
2
The other CRC is a 16-bit type, generated according to the standardized CRC16-polynomial function x + x + x
+ 1. This CRC is used for error detection when reading register pages or the datalog 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 16-bit CRC is always communicated in the inverted form. A CRCgenerator inside the DS1922L/T (Figure 15) calculates a new 16-bit CRC as shown in the command flow chart 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 flow chart, the 16-bit CRC value is the result of shifting the
command byte into the cleared CRC generator, followed by the 2 address bytes and the data bytes. The password
is excluded from the CRC calculation. Subsequent passes through the Read Memory with CRC flow chart 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 shifting in
the command code, the Target Addresses TA1 and TA2 and all the data bytes. The DS1922L/T transmits this CRC
only if the data bytes written to the scratchpad include scratchpad ending offset 11111b. The data may start at any
location within the scratchpad.
With the Read Scratchpad command the CRC is generated by first clearing the CRC generator and then shifting in
the command code, the Target Addresses TA1 and TA2, the E/S byte, and the scratchpad data starting at the
target address. The DS1922L/T transmits 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 see Application Note 27.
Figure 15. CRC-16 Hardware Description and Polynomial
16
Polynomial = X
st
nd
1
STAGE
0
th
8
2
X
th
10
STAGE
9
X
10
X
11
X
12
X
13
X
8
STAGE
7
X
th
14
STAGE
X
th
7
STAGE
6
X
th
13
STAGE
th
6
STAGE
5
X
th
12
STAGE
th
5
STAGE
4
X
th
11
STAGE
2
+X +1
th
4
STAGE
3
X
th
9
STAGE
th
3
STAGE
1
X
X
rd
2
STAGE
15
+X
th
15
STAGE
14
X
16
STAGE
15
X
INPUT DATA
42 of 48
16
X
CRC
OUTPUT
DS1922L/DS1922T
COMMAND-SPECIFIC 1-Wire COMMUNICATION PROTOCOL—LEGEND
SYMBOL
DESCRIPTION
RST
PD
Select
WS
RS
CPS
RMC
CM
FC
SM
STP
TA
TA-E/S
<data to EOS>
<data to EOP>
<data to EOM>
<PW/dummy>
<32 bytes>
<data>
FFh
CRC16\
FF loop
AA loop
1-Wire reset pulse generated by master
1-Wire presence pulse generated by slave
Command and data to satisfy the ROM function protocol
Command "Write Scratchpad"
Command "Read Scratchpad"
Command "Copy Scratchpad with Password"
Command "Read Memory with Password & CRC"
Command "Clear Memory with Password "
Command "Forced Conversion"
Command "Start Mission with Password"
Command "Stop Mission with Password"
Target Address TA1, TA2
Target Address TA1, TA2 with E/S byte
Transfer of as many data bytes as are needed to reach the scratchpad offset 1Fh
Transfer of as many data bytes as are needed to reach the end of a memory page
Transfer of as many data bytes as are needed to reach the end of the datalog memory
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
Transmission of one byte FFh
Transfer of an inverted CRC16
Indefinite loop where the master reads FF bytes
Indefinite loop where the master reads AA bytes
COMMAND-SPECIFIC 1-Wire COMMUNICATION PROTOCOL—COLOR CODES
Master to slave
Slave to master
WRITE SCRATCHPAD, REACHING THE END OF THE SCRATCHPAD (CANNOT FAIL)
RST
PD
Select
WS
TA
<data to EOS>
CRC16\
FF loop
READ SCRATCHPAD (CANNOT FAIL)
RST
PD
Select
RS
TA-E/S
<data to EOS>
CRC16\
COPY SCRATCHPAD WITH PASSWORD (SUCCESS)
RST
PD
Select
CPS
TA-E/S
<PW/dummy>
43 of 48
AA loop
FF loop
DS1922L/DS1922T
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>
CRC16\
<32 bytes>
CRC16\
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.
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.
44 of 48
DS1922L/DS1922T
MISSION EXAMPLE: PREPARE AND START A NEW MISSION
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 1: Clear the data of the previous mission
Step 2: Write the setup data to register page 1
Step 3: Start the mission
STEP 1
Clear the previous mission.
With only a single device connected to the bus master, the communication of step 1 looks like this:
MASTER MODE
TX
RX
TX
TX
TX
TX
TX
RX
DATA (LSB FIRST)
(Reset)
(Presence)
CCh
96h
<8 FFh bytes>
FFh
(Reset)
(Presence)
COMMENTS
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Clear Memory” command
Send dummy password
Send dummy byte
Reset pulse
Presence pulse
STEP 2
During the setup, the device needs to learn the following information:
§ Time and Date
§ Sample Rate
§ Alarm Thresholds
§ 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 will setup the DS1922L for a mission that logs temperature using 8-bit format. Such a mission
could last up to 56 days until the 8192-byte datalog memory is full.
ADDRESS
0200h
0201h
0202h
0203h
0204h
0205h
0206h
0207h
0208h
0209h
020Ah
020Bh
DATA
00h
30h
15h
01h
04h
02h
0Ah
00h
52h
66h
00h
FFh
EXAMPLE VALUES
15:30:00 hours
FUNCTION
Time
st
1 of April in 2002
Date
Every 10 minutes (EHSS = 0)
Sample rate
0°C low
10°C high
(Don’t care)
Temperature Alarm
Threshold
(Not applicable with DS1922L/T)
(Not applicable with DS1922L/T)
45 of 48
ADDRESS
020Ch
020Dh
020Eh
020Fh
0210h
0211h
0212h
DATA
FFh
FFh
FFh
FFh
02h
FCh
01h
0213h
0214h
0215h
0216h
0217h
0218h
C1h
FFh
FFh
5Ah
00h
00h
DS1922L/DS1922T
FUNCTION
EXAMPLE VALUES
(Don’t care)
Clock through
read-only registers
Enable high alarm
Disabled
On (enabled), EHSS = 0 (low sample rate)
Temperature Alarm Control
(Not applicable with DS1922L/T)
RTC Oscillator Control, sample
rate selection
General Mission Control
Clock through
read-only registers
Normal start; no rollover; 8-bit temp. log
(Don’t care)
90 minutes
Mission Start Delay
With only a single device connected to the bus master, the communication of step 2 looks like this:
MASTER MODE
TX
RX
TX
TX
TX
TX
TX
TX
TX
RX
TX
TX
RX
RX
RX
RX
TX
RX
TX
TX
TX
TX
TX
TX
TX
RX
DATA (LSB FIRST)
(Reset)
(Presence)
CCh
0Fh
00h
02h
<25 data bytes>
<7 FFh bytes>
(Reset)
(Presence)
CCh
AAh
00h
02h
1Fh
<32 data bytes>
(Reset)
(Presence)
CCh
99h
00h
02h
1Fh
<8 FFh bytes>
(Reset)
(Presence)
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COMMENTS
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Write Scratchpad” command
TA1, beginning offset = 00h
TA2, address = 0200h
Write 25 bytes of data to scratchpad
Write through the end of the scratchpad
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Read Scratchpad” command
Read TA1, beginning offset = 00h
Read TA2, address = 0200h
Read E/S, ending offset = 1Fh, flags = 0h
Read scratchpad data and verify
Reset pulse
Presence pulse
Issue “Skip ROM” command
Issue “Copy Scratchpad” command
TA1
TA2
(AUTHORIZATION CODE)
E/S
Send dummy password
Reset pulse
Presence pulse
DS1922L/DS1922T
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
DATA (LSB FIRST)
COMMENTS
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
TX
CCh
Issue “Skip ROM” command
TX
CCh
Issue “Start Mission” command
TX
<8 FFh bytes>
Send dummy password
TX
FFh
Send dummy byte
TX
(Reset)
Reset pulse
RX
(Presence)
Presence pulse
If step 3 was successful, the MIP bit in the General Status Register will be 1, the MEMCLR bit will be 0 and the
mission start delay will count down.
SOFTWARE CORRECTION ALGORITHM FOR TEMPERATURE
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). It consists of reference temperature (Tr) and conversion result (Tc) for two different temperatures, as shown below. See section Temperature Conversion for the binary
number format.
ADDRESS
0240h
0241h
0242h
0243h
0244h
0245h
0246h
0247h
DESIGNATOR
Tr2H
Tr2L
Tc2H
Tc2L
Tr3H
Tr3L
Tc3H
Tc3L
DESCRIPTION
Cold reference temperature, high-byte
Cold reference temperature, low-byte
Conversion result at cold reference temperature, high-byte
Conversion result at cold reference temperature, low-byte
Hot reference temperature, high-byte
Hot reference temperature, low-byte
Conversion result at hot reference temperature, high-byte
Conversion result at hot reference temperature, low-byte
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.
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 right 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 low/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.
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DS1922L/DS1922T
STEP 1, PREPARATION
Read the 64-bit ROM to obtain the family code. If family code ¹ 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
2
2
2
2
2
2
B = (Tr2 - Tr1 ) * (Err3 - Err1)/[(Tr2 - Tr1 ) * (Tr3 - Tr1) + (Tr3 - Tr1 ) * (Tr1 - Tr2)]
2
2
A = B * (Tr1 – Tr2) / (Tr2 - Tr1 )
2
C = Err1 - A * Tr1 - B * Tr1
STEP 2, EXECUTION
Tc = TcH/2 + TcL/512 - Offset
2
Tcorr = Tc - (A * Tc + B * Tc + C)
(convert from binary to °C)
(the actual correction)
Numerical Correction Example
Converted data from Calibration Memory
Tr1 = 60°C
Tr2 = -10.1297°C
Tr3 = 24.6483°C
Tc2 = -10.0625°C
Tc3 = 24.5°C
Resulting Correction Coefficients
B = -0.008741
A = 0.000175/°C
C = -0.039332°C
Error values
Err2 = 0.0672°C
Err3 = -0.1483°C
Err1 = 0.0672°C
Application of Correction Coefficients to sample reading
Tc = 22.500°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.
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