A bq2060A-based battery pack that has been in production for 10 years suddenly seems to be having problems with HDQ writes to VCell2. Are there any conditions where writes to that register could be inhibited?
Background: the battery pack uses the SMBus lines for communication with the customer's Host Processor, the HDQ line is used for communications with the power module we manufacture along with the battery pack. The power module contains a PIC16F876 for control and HDQ communications and is capable of doing a system shutdown when commanded by the customer's Host Processor. The Host processor has no direct communication with the power module controller, so it uses values written to Vcell 1 and Vcell 2 in the fuel gauge memory as status flags. When the power module sees the flag set in the Vcell2 register, it will send a shutdown command after writing a zero to Vcell2 and verifying that write with a read-back to make sure the request has been cleared. We are experiencing some power module-battery pack combinations where the write to Vcell2 is not working and the verifying read-back is unsuccessful causing the shutdown not to happen.
Since the HDQ reads all work fine, I don't see a obvious hardware issue that could cause an inability to write to Vcell2. Are there battery voltage or status conditions that could inhibit the ability to write to this register?
