DS1977-F5- MAXIM [Maxim Integrated Products], DS1977-F5- Datasheet - Page 5

• Manufacturer Part Number: DS1977-F5-
• Description: Password-Protected 32KB EEPROM iButton
• Manufacturer: MAXIM [Maxim Integrated Products]

Figure 2. HIERARCHICAL STRUCTURE FOR 1-WIRE PROTOCOL
64-BIT LASERED ROM
Each DS1977 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 and XOR gates as shown in Figure 4.
The polynomial is X
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
time is shifted in. After the 8
48
CRC returns the Shift register to all 0s.
Figure 3. 64-BIT LASERED ROM
MSB
MSB
th
CRC CODE
bit of the serial number has been entered, the Shift register contains the CRC value. Shifting in the 8 bits of
8-BIT
MASTER
COMMAND
LEVEL:
BUS
LSB
1-Wire ROM FUNCTION
MEMORY FUNCTION
DS1977-SPECIFIC
COMMANDS
COMMANDS
MSB
8
+ X
5
+ X
th
4
bit of the family code has been entered, then the serial number is entered. After the
+ 1. Additional information about the 1-Wire Cyclic Redundancy Check is available
1-Wire NET
48-BIT SERIAL NUMBER
DS1977
AVAILABLE
COMMANDS:
READ ROM
MATCH ROM
SEARCH ROM
SKIP ROM
RESUME
OVERDRIVE SKIP
OVERDRIVE MATCH
WRITE SCRATCHPAD
READ SCRATCHPAD
COPY SCRATCHPAD
W/PW
READ MEMORY W/PW
VERIFY PASSWORD
READ VERSION
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DEVICES
DATA FIELD
AFFECTED:
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
64-BIT ROM, RC-FLAG
RC-FLAG
RC-FLAG
RC-FLAG, OD-FLAG
64-BIT ROM, RC-FLAG, OD-FLAG
64-BYTE SCRATCHPAD
64-BYTE SCRATCHPAD
DATA MEMORY, PASSWORDS,
DATA MEMORY, PASSWORDS,
PASSWORDS
VERSION REGISTER
OTHER
PASSWORD ENABLE BYTE
PASSWORD ENABLE BYTE
LSB
MSB
8-BIT FAMILY
CODE (37h)
LSB
LSB
DS1977