DS2781 Maxim Integrated Products, DS2781 Datasheet - Page 23

• Manufacturer Part Number: DS2781
• Description: 1-Cell or 2-Cell Standalone Fuel Gauge IC
• Manufacturer: Maxim Integrated Products

Table 3. PARAMETER EEPROM MEMORY BLOCK 1
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 DS2781 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 DS2781 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 (3Dh for DS2781). 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 18). The 64-bit net address and the 1-Wire I/O
circuitry built into the device enable the DS2781 to communicate through the 1-Wire protocol detailed in the 1-Wire
Bus System section of this data sheet.
Figure 18. 1-Wire Net Address Format
CRC GENERATION
The DS2781 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 DS2781. The host system is responsible for verifying the CRC value and taking
action as a result. The DS2781 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 18, or it can be generated in software. Additional information about the Dallas 1-Wire CRC is available in
ADDRESS
(HEX)
6C
6D
60
61
62
63
64
65
66
67
68
69
6A
6B
6E
6F
CONTROL - Control Register
AB - Accumulation Bias
AC - Aging Capacity MSB
AC - Aging Capacity LSB
VCHG - Charge Voltage
IMIN - Minimum Charge Current
VAE - Active Empty Voltage
IAE - Active Empty Current
Active Empty 40
RSNSP - Sense Resistor Prime
Full 40 MSB
Full 40 LSB
Full Segment 4 Slope
Full Segment 3 Slope
Full Segment 2 Slope
Full Segment 1 Slope
8-BIT CRC
MSb
DESCRIPTION
48-BIT SERIAL NUMBER
23 of 30
ADDRESS
(HEX)
7C
7D
7A
7B
7E
70
71
72
73
74
75
76
77
78
79
7F
AE Segment 4 Slope
AE Segment 3 Slope
AE Segment 2 Slope
AE Segment 1 Slope
SE Segment 4 Slope
SE Segment 3 Slope
SE Segment 2 Slope
SE Segment 1 Slope
RSGAIN - Sense Resistor Gain MSB
RSGAIN - Sense Resistor Gain LSB
RSTC - Sense Resistor Temp. Coeff.
COB – Current Offset Bias
TBP34
TBP23
TBP12
Reserved
8-BIT FAMILY
CODE (3Dh)
DESCRIPTION
LSb