Rainbow-electronics DS2781 Bedienungsanleitung PDF herunterladen (Seite 23)

DS2781: Two-Cell Standalone Fuel Gauge IC

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Table 3. PARAMETER EEPROM MEMORY BLOCK 1

ADDRESS

(HEX)

DESCRIPTION

ADDRESS

(HEX)

DESCRIPTION

CONTROL - Control Register

70 AE Segment 4 Slope

AB - Accumulation Bias

71 AE Segment 3 Slope

AC - Aging Capacity MSB

72 AE Segment 2 Slope

AC - Aging Capacity LSB

73 AE Segment 1 Slope

VCHG - Charge Voltage

74 SE Segment 4 Slope

IMIN - Minimum Charge Current

75 SE Segment 3 Slope

VAE - Active Empty Voltage

76 SE Segment 2 Slope

IAE - Active Empty Current

77 SE Segment 1 Slope

68 Active Empty 40 78

RSGAIN - Sense Resistor Gain MSB

RSNSP - Sense Resistor Prime

RSGAIN - Sense Resistor Gain LSB

6A Full 40 MSB 7A

RSTC - Sense Resistor Temp. Coeff.

6B Full 40 LSB 7B

COB – Current Offset Bias

6C Full Segment 4 Slope 7C

TBP34

6D Full Segment 3 Slope 7D

TBP23

6E Full Segment 2 Slope 7E

TBP12

6F Full Segment 1 Slope 7F Reserved

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

8-BIT CRC 48-BIT SERIAL NUMBER

8-BIT FAMILY

CODE (3Dh)

MSb LSb

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

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