
DS1923
iButton Hygrochron Temperature/Humidity
Logger with 8KB Data-Log Memory
64-Bit Lasered ROM
Each DS1923 contains a unique ROM code that is 64
bits long. The first 8 bits are a 1-Wire family code. The
next 48 bits are a unique serial number. The last 8 bits
are a cyclic redundancy check (CRC) of the first 56 bits
(see Figure 3 for details). The 1-Wire CRC is generated
using a polynomial generator consisting of a shift regis-
ter and XOR gates as shown in Figure 4. The polynomi-
al is X 8 + X 5 + X 4 + 1. Additional information about the
1-Wire CRC is available in Application Note 27:
Understanding and Using Cyclic Redundancy Checks
with Maxim iButton Products.
The shift register bits are initialized to 0. Then, starting
with the least significant bit of the family code, one bit
at a time is shifted in. After the 8th bit of the family code
has been entered, the serial number is entered. After
the last bit of the serial number has been entered, the
shift register contains the CRC value. Shifting in the 8
bits of CRC returns the shift register to all 0s.
BUS
MASTER
1-Wire NET
OTHER DEVICES
DS1923
COMMAND LEVEL:
1-Wire ROM
FUNCTION COMMANDS
DS1923-SPECIFIC
MEMORY/CONTROL FUNCTION
COMMANDS
AVAILABLE COMMANDS:
READ ROM
MATCH ROM
SEARCH ROM
CONDITIONAL SEARCH ROM
SKIP ROM
RESUME
OVERDRIVE-SKIP ROM
OVERDRIVE-MATCH ROM
WRITE SCRATCHPAD
READ SCRATCHPAD
COPY SCRATCHPAD WITH PW
READ MEMORY WITH PW AND CRC
CLEAR MEMORY WITH PW
FORCED CONVERSION
START MISSION WITH PW
STOP MISSION WITH PW
DATA FIELD AFFECTED:
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
256-BIT SCRATCHPAD, FLAGS
256-BIT SCRATCHPAD
512-BYTE DATA MEMORY, REGISTERS, FLAGS, PASSWORDS
MEMORY, REGISTERS, PASSWORDS
MISSION TIMESTAMP, MISSION SAMPLES COUNTER,
START DELAY, ALARM FLAGS, PASSWORDS
MEMORY ADDRESSES 020Ch TO 020Fh
FLAGS, TIMESTAMP, MEMORY ADDRESSES
020Ch TO 020Fh (WHEN LOGGING)
FLAGS
Figure 2. Hierarchical Structure for 1-Wire Protocol
MSB
LSB
8-BIT
CRC CODE
48-BIT SERIAL NUMBER
8-BIT FAMILY CODE
(41h)
MSB
LSB MSB
LSB MSB
LSB
Figure 3. 64-Bit Lasered ROM
Maxim Integrated
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