your tris is upside down!  0x38 ( b'00111000' ) sets the 1's as inputs and
the 0's as outputs.

HOT TIP: (well, tip) use binary notation rather than hex for tris type
commands, the 1s and 0s look like Is and Os too, it's also easier to see
which pin is which.

You need, b'00000111' or 0x07

Also in loop, you are checking GPIO,3 - should this be a different pin? You
comment at the beginning says set 0,1,2 as input, but your comment later
says read 3 as input.........


Garage door warming system eh? What luxury! or is that a typo for warning?


Regards, Kevin

-----Original Message-----
From: pic microcontroller discussion list
[mailto:PICLIST@MITVMA.MIT.EDU]On Behalf Of Fok, Ben
Sent: 14 August 2001 16:14
To: PICLIST@MITVMA.MIT.EDU
Subject: [PIC]: Need help on PIC12C508A programming


I am working on a little project using the 12C508A.  It is a garage door
warming system.  The Pic is connected to a buzzer and two LEDs (GPIO 2), one
red(GPIO 0) and one green(GPIO 1).  I want use GPIO 3/MCLR/Vpp for
detection.  Here is a short program I wrote:

start:          org     0x00
                movlw   0x38
                tris    gpio            ;set gpio 0, 1, 2 as input and the
rest as output
                movlw   0x3f
                option                  ;enable weak pullup and wake on pin
change, bit 6 and 7
loop:           btfsc   gpio, 3         ;check and see if gpio 3 is low
                goto    loop            ;if not check again
                call    buzzer          ;make the buzzer buzz
                goto    start

When I program the PIC I use LP crystal, internal MCLR and no watchdog.

The problem I have is gpio 3 is acting as an input pin.  I don't know how to
debug it because the ICE doesn't emulate that pin.

Please help.

Ben

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