BQ2085-V1P2 Datasheet, PDF (22/56 Pages) Texas Instruments – SBS-COMPLIANT GAS GAUGE IC FOR USE WITH THE bq29311

bq2085−V1P2
SLUS590 − DECEMBER 2003
PEC Protocol (Continued)
1
7
1
ÓÓÓÓ ÓÓÓÓ ÓÓÓÓ ÓÓÓÓ _S
Battery Address
0001011
0
1
8
1
A Command Code A
8
Data Byte Low
1
8
1
A Data Byte High A
Write Word
1
7
11
8
11
7
11
ÓÓÓÓ ÓÓÓÓ ÓÓÓÓÓÓ _S
Battery Address
0001011
0
A Command Code A
S Battery Address 1
A
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8
PEC
11
ÓÓÓÓ_{A P}
8
1
8
1
ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ _{Data Byte Low A Data Byte High A}
8
PEC
11
AP
Read Word
1
7
11
8
11
7
11
ÓÓ ÓÓ ÓÓ S ^{Battery Address} 0 A Command Code A S Battery Address 1 A
ÓÓ ÓÓ ÓÓ ^0001011
ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ ÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓÓ ⁸
1
Byte Count = N A
8
1
Data Byte 1 A
8
1
Data Byte 2 A
8
1
Data Byte N A
8
PEC
11
AP
Block Read
ÓÓÓÓHost Processor
bq2085
A − ACKNOWLEDGE
A − NOT ACKNOWLEDGE
S − START
P − STOP
Figure 7. SMBus Communication Protocol With PEC
PEC Calculation
The basis of the PEC calculation is an 8-bit cyclic redundancy check (CRC-8) based on the polynomial
C(X) = X8 + X2 + X1 + 1. The PEC calculation includes all bytes in the transmission, including address,
command, and data. The PEC calculation does not include ACKNOWLEDGE, NOT ACKNOWLEDGE, start,
stop, and repeated start bits.
For example, the host requests RemainingCapacity( ) from the bq2085−V1P2. This includes the host following
the read word protocol. The bq2085−V1P2 calculates the PEC based on the following 5 bytes of data, assuming
the remaining capacity of the battery is 1001 mAh.
D Battery address with R/W = 0: 0x16
D Command code for RemainingCapacity( ): 0x0f
D Battery address with R/W = 1: 0x17
D RemainingCapacity( ): 0x03e9
For 0x160f17e903, the bq2085−V1P2 transmits a PEC of 0xe8 to the host.
PEC Enable in Master Mode
PEC for master mode broadcasts to the charger, host, or both can be enabled/disabled with the combination
of the bits HPE and CPE in Pack Configuration DF 0x28.
SMBus On and Off State
The bq2085−V1P2 detects whether the SMBus enters the Off State by monitoring the SMBC and SMBD lines.
When both signals are continually low for at least 2.0 s, the bq2085−V1P2 detects the Off State. When the
SMBC and SMBD lines go high, the bq2085−V1P2 detects the On state and can begin communication within
1 ms. One-MΩ pulldown resistors on SMBC and SMBD are recommended for reliable Off state detection.
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