Are the RTC backup registers guaranteed to be zero?

[Patrick Morwald]

Hi,

when the backup power domain gets reset, are the RTC backup registers guaranteed to be zero or can they be any arbitrary value?

[T J]

Generally the whole point of a battery backed ram is to save the ram contents.

Usually there is no "Zero" hardware functionality, only a program solution you would create.

for a known stable state, use the last two bytes as a checksum of the entire backupRam-2 bytes

then you will know if your array has been cleared and initialised or else it needs clearing, and add checksum.

[Patrick Morwald]

Ok thanks for the idea with the checksum. Maybe i did formulate my question not right, i meant the condition of the backup registers after there was no power at all to the whole Chip, including no backup power.

Thanks anyways!

[T J]

I believe the data will be randomly set on a virgin power up.