MCP7940.adjust() function reset the PWRFAIL and VBATEN

Question

MCP7940.adjust() function reset the PWRFAIL and VBATEN

Closed this issue 6 years ago · 2 comments

The adjust() function resets the RTCWDAY, PWRFAIL bit and VBATEN bit somehow; this function should only affect the WDAY2-WDAY0 bits?

So if you use a backup battery and multiple adjust() functions in the main loop, the battery will be disabled whenever you call the adjust() function moving forward.

Answer 1 · 2018-12-15T08:56:54.000Z

Looking into the possible causes of this problem

Answer 2 · 2018-12-15T09:09:47.000Z

When the library sets the weekday, it cleared the OSCRUN, VBATEN and PWRFAIL register bits which caused the error. The fix is to only set the 3 relevant bits for the DOW and leave the rest of the register unchanged. Good catch!