RTC won't run from Vbatt

lhoy · ‎2009-03-25

Posted on March 26, 2009 at 03:31

lhoy · ‎2011-05-17

Posted on May 17, 2011 at 11:32

I have built five identical CPU boards using a STR912FAW44X6. Each has a backup battery to keep the RTC running when the main power is off. Of the five, one will not keep time when the power is off. From oscilliscope observations of the X1_RTC and X2_RTC pins, it appears that the RTC on this one board is loosing power when the main power goes off despite the connection of Vbatt to a 3v backup battery. I have verified the electrical connection of the battery to the Vbatt pin (no bad solder joints) and the CPU programs and executes correctly except for this one problem. I have also performed a full chip erase and reprogram but with no change in the RTC behaviour. Question: Is there any programable bit in the CPU that may prevent the RTC from running from Vbatt? Are there any other things I should try before attempting to replace the CPU chip?

kairos · ‎2011-05-17

Posted on May 17, 2011 at 11:32

1)By configuring the PWR bit in the

RTC_CR register, you can select to power only the RTC or both the RTC and the SRAM from VBATT.

2)Have u Selected the Option mentioned above,if so see if u are modifying the RTC CONTROL REGISTER after Enabling that PWR Pin in RTC->CR anywhere else.Make sure RTC->CR |= 0x80;

3)Check The Battery if it is showing required voltage or not.