bq20z80-V101
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SLUS625D–SEPTEMBER 2004–REVISED OCTOBER 2005
COMMUNICATIONS
The bq20z80 uses SMBus v1.1 with Master Mode and package error checking (PEC) options per the SBS
specification.
SMBus On and Off State
The bq20z80 detects an SMBus off state when SMBC and SMBD are logic-low for ≥ 2 seconds. Clearing this
state requires either SMBC or SMBD to transition high. Within 1 ms, the communication bus is available.
Packet Error Checking
The bq20z80 can receive or transmit data with or without PEC.
In the read-word protocol, the bq20z80 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 bq20z80
compares the value to its calculation. If the PEC is correct, the bq20z80 responds with an ACKNOWLEDGE. If it
is not correct, the bq20z80 responds with a NOT ACKNOWLEDGE and sets an error code.
In the write-word and block-read in master mode, the host generates an ACKNOWLEDGE after the last byte of
data sent by the bq20z80. The bq20z80 then sends the PEC, and the host, acting as a master-receiver,
generates a NOT ACKNOWLEDGE and a stop condition.
Gas Gauge
Figure 1. SMBus Communication Protocol Without PEC
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