Datasheet
DS2762 High-Precision Li+ Battery Monitor With Alerts
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1-Wire BUS SYSTEM
The 1-Wire bus is a system that has a single bus master and one or more slaves. A multidrop bus is a 1-Wire bus
with multiple slaves. A single-drop bus has only one slave device. In all instances, the DS2762 is a slave device.
The bus master is typically a microprocessor in the host system. The discussion of this bus system consists of four
topics: 64-bit net address, hardware configuration, transaction sequence, and 1-Wire signaling.
64-BIT NET ADDRESS
Each DS2762 has a unique, factory-programmed 1-Wire net address that is 64 bits in length. The first eight bits are
the 1-Wire family code (30h for DS2762). The next 48 bits are a unique serial number. The last eight bits are a
cyclic redundancy check (CRC) of the first 56 bits (see Figure 14). The 64-bit net address and the 1-Wire I/O
circuitry built into the device enable the DS2762 to communicate through the 1-Wire protocol detailed in the 1-Wire
Bus System section of this data sheet.
Figure 14. 1-Wire Net Address Format
8-BIT CRC 48-BIT SERIAL NUMBER
8-BIT FAMILY
CODE (30H)
MSb LSb
CRC GENERATION
The DS2762 has an 8-bit CRC stored in the most significant byte of its 1-Wire net address. To ensure error-free
transmission of the address, the host system can compute a CRC value from the first 56 bits of the address and
compare it to the CRC from the DS2762. The host system is responsible for verifying the CRC value and taking
action as a result. The DS2762 does not compare CRC values and does not prevent a command sequence from
proceeding as a result of a CRC mismatch. Proper use of the CRC can result in a communication channel with a
very high level of integrity.
The CRC can be generated by the host using a circuit consisting of a shift register and XOR gates as shown in
Figure 15, or it can be generated in software. Additional information about the Dallas 1-Wire CRC is available in
Application Note 27: Understanding and Using Cyclic Redundancy Checks with Dallas Semiconductor Touch
Memory Products (www.maxim-ic.com/appnoteindex
).
In the circuit in Figure 15, 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 serial
number is entered. After the 48th bit of the serial number has been entered, the shift register contains the CRC
value.
Figure 15. 1-Wire CRC Generation Block Diagram
MSb
XOR
XOR
LSb
XOR
INPUT