BQ2085 Datasheet, PDF (21/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085
SLUS541 – OCTOBER 2002
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 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 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 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
compares the value to its calculation. If the PEC is correct, the bq2085 responds with an ACKNOWLEDGE. If
it is not correct, the bq2085 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. The bq2085 then sends the PEC and the host acting as a master-receiver generates a NOT
ACKNOWLEDGE and a stop condition.
1
7
11
8
1
ÎÎÎÎ ÎÎÎÎ ÎÎÎÎ ÎÎÎÎ _S
Battery Address
0001011
0
A Command Code
A
ÎÎ ÎÎ ÎÎ ÎÎ Write Word
8
Data Byte Low
1
8
11
A Data Byte High A P
1
7
S
Battery Address
0001011
11
8
11
7
ÎÎÎÎ ÎÎÎÎ _{0 A Command Code A S Battery Address}
11
ÎÎÎÎ _{1 A}
8
1
8
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ _{Data Byte Low A Data Byte High}
1
AP
Read Word
1
7
S
Battery Address
0001011
11
8
11
7
ÎÎÎÎ ÎÎÎÎ 0 A Command Code A S Battery Address
11
ÎÎÎÎ 1 A
8
1
ÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎÎ ÎÎÎÎÎÎÎÎÎÎÎÎ _{ByteCount= N A}
8
1
Data Byte 1 A
8
1
Data Byte 2 A
8
Data Byte N
11
AP
Block Read
Host Processor
ÎÎÎÎ^bq2083
A – ACKNOWLEDGE
A – NOT ACKNOWLEDGE
S – START
P – STOP
Figure 6. SMBus Communication Protocol Without PEC
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