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Battery Management - Gas Gauge Forum
A general rule of setting the two-word keys for your gas gauge
In bq20zxx (bq20z80, z70, z75, z95, z90, etc) devices, when setting the two-word keys, remember to have a unique first word among the keys. Currently, PF Clear, Unseal, and Full-access keys belong to the two-word key category.
The general rule is the first word of any 32-bit key cannot be the same. This reason is that the comm routine receives one 16-bit word at a time. The first word "arms" the security check that matches its first word, and cause it to look for the second word. Since the security checks are checked in sequence, the first check that matches the first word will be "armed".
For example, if your Unseal Key is 0x1234 and 0x5678, and your PF Clear key is 0x1234 and 0x4321, and then because the first word of these two keys are the same, you will either not able to unseal or not able to clear the PF failure.
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