DS1923 Maxim, DS1923 Datasheet - Page 13

• Manufacturer Part Number: DS1923
• Description: The DS1923 temperature/humidity logger iButton® is a rugged, self-sufficient system that measures temperature and/or humidity and records the result in a protected memory section
• Manufacturer: Maxim

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
1-Wire CRC is available in Application Note 27:
Figure 2. Hierarchical Structure for 1-Wire Protocol
Figure 3. 64-Bit Lasered ROM
8
+ X
MSB
MSB
MASTER
5
BUS
+ X
Hygrochron Temperature/Humidity Logger
MEMORY/CONTROL FUNCTION
CRC CODE
8-BIT
FUNCTION COMMANDS
4
COMMAND LEVEL:
______________________________________________________________________________________
DS1923-SPECIFIC
+ 1. Additional information about the
COMMANDS
1-Wire ROM
LSB
MSB
64-Bit Lasered ROM
iButton with 8KB Data-Log Memory
1-Wire NET
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
OTHER DEVICES
48-BIT SERIAL NUMBER
DS1923
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.
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,
MEMORY ADDRESSES 020Ch TO 020Fh
FLAGS, TIMESTAMP, MEMORY ADDRESSES
FLAGS
START DELAY, ALARM FLAGS, PASSWORDS
020Ch TO 020Fh (WHEN LOGGING)
LSB
MSB
8-BIT FAMILY CODE
(41h)
LSB
LSB
13