brownout configuration

[dave.t]

Hi all
I am trying to understand how the brownout facility is implemented - I am using the 12f629.
The data sheets say that the user must set the BOD to a '1' as its state is unknown on reset and checked on subsequent resets to establish if a 'brownout' has occured ie. BOD is '0'.
How can I distinguish between a 'power on reset' and a 'brownout'if the state of BOD bit is unknown.

If I set the BOD bit to a '1' then I must check on any reset for it changing to a '0' before - I set it to a known state ('1') (otherwise BOD would always be '1') but then I would be checking a unknown state bit!
I am sure it is simple but I think my brain has stuck in reverse!
Many thanks
Dave
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This message was ported from CCS's old forum
Original Post ID: 144515550

[R.J.Hamlett]

:=Hi all
:=I am trying to understand how the brownout facility is implemented - I am using the 12f629.
:=The data sheets say that the user must set the BOD to a '1' as its state is unknown on reset and checked on subsequent resets to establish if a 'brownout' has occured ie. BOD is '0'.
:=How can I distinguish between a 'power on reset' and a 'brownout'if the state of BOD bit is unknown.
:=
:=If I set the BOD bit to a '1' then I must check on any reset for it changing to a '0' before - I set it to a known state ('1') (otherwise BOD would always be '1') but then I would be checking a unknown state bit!
:=I am sure it is simple but I think my brain has stuck in reverse!
:=Many thanks
:=Dave
The 'key', is the POR bit.
The first time the chip is powered up, the POR bit will be zero (this is defined). Now at this point, you can set the BOR bit, and in future, can now tell when a brownout has occurred. You are correct, that "on it's own", testing just the brownout bit, owuld leave you unable to tell what has happened.

Best Wishes
___________________________
This message was ported from CCS's old forum
Original Post ID: 144515552