The TI BQ20Z655 gas gauge device is used on a battery pack system. The battery pack also has a TI BQ24765 battery charger. Both the BQ20Z655 and BQ24765 devices communicate with an Actel FPGA over an I2C/SMB bus. Under normal conditions, the FPGA operates as master of the I2C/SMBus. However, we have observed the BQ20Z655 broadcasting a message to the battery charger as a Master. The broadcast message occurs once every ~50sec. The problem is that we are seeing intermittent failed I2C/SMBus reads (FPGA reading BQ20Z655) that we have isolated down to what we believe is a multi-master bus collision between the FPGA and the BQ20Z655. When we use the [BCAST] bit to disable the broadcasts, the failures go away. The FPGA I2C core is supposed to support multi-master operation. We believe that the BQ20Z655 should handle multi-master as well (although it is never explicitly stated in the datasheet). But, we did notice that there was a change notice in Oct’11 (see attachment) changing the part to a –R1 revision. Part of this revision addressed a problem related to multi-master mode. What we are trying to find out is whether or not there are any known issues with SMBus multi-master mode on the BQ20Z655.
0743.bq20z655_R1-Change Notice slua623.pdf
Additionally, we would like to find out if there a way to determine if we have the latest –R1 firmware.
