BQ2084-V140_14 Datasheet, PDF (30/64 Pages) Texas Instruments – SBS v1.1-COMPLIANT GAS GAUGE FOR USE WITH THE bq29312

bq2084-V140
SLUS664B – JULY 2005 – REVISED AUGUST 2006
www.ti.com
Gas Gauge
Figure 6. 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 bq2084-V140. This includes the host following the
read word protocol. The bq2084-V140 calculates the PEC based on the following 5 bytes of data, assuming the
remaining capacity of the battery is 1001 mAh.
• Battery Address with R/W = 0: 0x16
• Command Code for RemainingCapacity(): 0x0f
• Battery Address with R/W = 1: 0x17
• RemainingCapacity(): 0x03e9
For 0x160f17e903, the bq2084-V140 transmits a PEC of 0xe8 to the host.
PEC Enable in Master Mode
The 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 bq2084-V140 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 bq2084-V140 detects the Off State. When the
SMBC and SMBD lines go high, the bq2084-V140 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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