AnsweredAssumed Answered

'908JL3  0,PORTB always reads as low

Question asked by Guest on Jul 15, 2009
Latest reply on Jul 16, 2009 by Graham Pratt

Got a =very= basic problem that is just driving me nuts.

Using a '908JL3 and going around in a loop polling the port B inputs and when one

of them is low it jumps off to flash a LED then comes back and starts polling again.

This program doesn't really do anything; it just runs the piece of code that is causing the

trouble. Something like this:


                    MOV    #%00000000,DDRB


TOP             BRCLR    3,PORTB,LED

                   BRCLR    2,PORTB,LED

                   BRCLR    1,PORTB,LED

                   BRCLR    0,PORTB,LED

                   JMP         TOP


LED            <FLASH LED ONCE>

                   JMP         TOP


B3, B2, B1work just fine but B0 no way can I get it to work properly. It is always read as

if it were clear  and branches accordingly.  I tried a second MCU and then a third with a datecode 2 years earlier and still the same. Have these things got a bug or something?

It was getting to the stage I was looking around for hidden cameras, thinking someone

was playing some kind of practical joke on me. Puta scope on the pins and they go down

at the right time so it is not a board fault. This is SO stupid. 


Anybody have any ideas?