pic18f86j90 RB4 and RB5 pullups are read as 0

[[email protected]]

Hi,

I am using pic18f86j90 with CCS ver 4.099.

My firmware has some basic inits (like ports, A/D and some more modules) and then comes the following code:

if ((input(HW_KEY_OK) == 0)&&(input(HW_KEY_AUTO) == 0))
{
DigitDisplay(CHR_R, CHR_S, CHR_T);
ResetEEprom();
DigitDisplay(CHR_E, CHR_N, CHR__d);
}

HW_KEY_OK is RB4 and HW_KEY_AUTO is RB5 with pullups enabled.

The problem: while both switchs(HW_KEY_OK and HW_KEY_AUTO) are not pressed sometimes the code inside the "if" is executed and sometimes not. This is driving me crazy.

I looked at the RB4,RB5 signals using oscilloscope and they are always high (pulled-up) even when problem occurs.

Does someone have a clue what's going on here?

Regards,
Gil
_________________
Gil F.

[Ttelmah]

They are probably not reliably high.

The internal pull-ups are very low current sources. Just 30uA typically. It doesn't take much EMI, for a line pulled up with this small current, to be momentarily taken low enough to not be seen as 'high'.
Are you absolutely sure you are enabling the pull-ups?. You realise 'TRUE' would not enable them?. They are per bit settable on this chip.

[[email protected]]

Sorry for misleading. The error is not in the code displayed above.

Case closed
_________________
Gil F.