Rainbow Electronics DS28EA00 - Manual (Page 6)

DS28EA00 1-Wire Digital Thermometer with Sequence Detect and PIO
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64-BIT REGISTRATION NUMBER
Each DS28EA00 contains a unique Registration Number 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 Figure 4. The polynomial is X
8
+ X
5
+ X
4
+ 1. Additional information about the Dallas 1-Wire Cyclic
Redundancy Check (CRC) is available in Application Note 27.
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, then the 48-bit serial number is entered.
After the last byte 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.
Figure 2. Hierachical Structure for 1-Wire Protocol
DS28EA00
Available
Commands: Command
Level: Data Field
Affected:
1-Wire ROM Function
Commands (see Figure 12)
Read ROM
Match ROM
Search ROM
Conditional Search
ROM
Conditional Read
ROM
Skip ROM
Overdrive Skip
Overdrive Match
64-bit Reg. #
64-bit Reg. #
64-bit Reg. #
64-bit Reg. #, Temperature Alarm
Registers, Scratchpad
64-bit Reg. #, PIOB pin state, Chain
state
(none)
64-bit Reg. #, OD-Flag
64-bit Reg. #, OD-Flag
Device-Specific
Control Function
Commands (see Figure 10)
Write Scratchpad
Read Scratchpad
Copy Scratchpad
Convert Temperature
Read Power Mode
Recall EEPROM
PIO Access Read
PIO Access Write
Chain Scratchpad
Scratchpad
Temperature Alarm and Configuration
Registers
Scratchpad, Temperature Alarm
Registers
V
DD
pin voltage
Scratchpad, Temperature Alarm and
Configuration Registers
PIO pins
PIO pins
Chain state, PIOA pin state
Figure 3. 64-Bit Registration Number
MSB LSB
8-Bit
CRC Code
48-Bit Serial Number
8-Bit Family
Code (42h)
MSB LSB MSB LSB MSB LSB