BQ2085-V1P2 Datasheet, PDF (20/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085−V1P2
SLUS590 − DECEMBER 2003
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by the SMBus command code or output the data from the specified register. The processor completes the
access with a stop condition. A stop condition consists of a low-to-high transition of the SMBD line while the
SMBC is high. With SMBus, the most-significant bit (MSB) of a data byte is transmitted first.
In some instances, the bq2085−V1P2 acts as the bus master. This occurs when the bq2085−V1P2 broadcasts
charging requirements and alarm conditions to device addresses 0x12 (SBS smart charger) and 0x10 (SBS
host controller.)
SMBus Protocol
The bq2085−V1P2 supports the following SMBus protocols:
D Read word
D Write word
D Block read
A processor acting as the bus master uses the three protocols to communicate with the bq2085−V1P2. The
bq2085−V1P2 acting as the bus master uses the write word protocol.
The SMBD and SMBC pins are open drain and require external pullup resistors. A 1-MΩ pulldown resistor in
the battery pack on SMBC and SMBD is required to assure the detection of the SMBus offstate, the
performance of automatic offset calibration, and the initiation of the low-power sleep mode when the battery
pack is removed.
SMBus Packet Error Checking
The bq2085−V1P2 supports packet error checking as a mechanism to confirm proper communication between
it and another SMBus device. Packet error checking requires that both the transmitter and receiver calculate
a packet error code (PEC) for each communication message. The device that supplies the last byte in the
communication message appends the PEC to the message. The receiver compares the transmitted PEC to
its PEC result to determine if there is a communication error.
PEC Protocol
The bq2085−V1P2 can receive or transmit data with or without PEC. Figure 6 shows the communication
protocol for the read word, write word, and read block messages without PEC. Figure 7 includes PEC.
In the read word protocol, the bq2085−V1P2 receives the PEC after the last byte of data from the host. If the
host does not support PEC, the last byte of data is followed by a stop condition. After receipt of the PEC, the
bq2085−V1P2 compares the value to its calculation. If the PEC is correct, the bq2085−V1P2 responds with an
ACKNOWLEDGE. If it is not correct, the bq2085−V1P2 responds with a NOT ACKNOWLEDGE and sets an
error code.
In the write word and block read, the host generates an ACKNOWLEDGE after the last byte of data sent by
the bq2085−V1P2. The bq2085−V1P2 then sends the PEC and the host acting as a master-receiver generates
a NOT ACKNOWLEDGE and a stop condition.
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