Input GP3 not responding when programming the 12F508
I have used the PICSTART PLUS for several years and had great success in designing numerous projects. Recently I purchased the PicKit4 and switched to using MPLAB X version 5.10. On my first simple test project, using the Microchip 12F508, it worked very well except for the input GP3. I know that this pin is labeled as GP3/ MCLR /Vpp but I am unable to get it to respond as an input GP3. I have tried setting the MCLR in CONFIG both ON and OFF without getting the required response.
1. When I set the MCLR in CONFIG to OFF, GP3 (pin 4) sees a high even when it is connected to low through a 1K resistor.
2. When I set the MCLR in CONFIG to ON, GP3 constantly sees a low even though it is connected to a high through a 10K + 1K resistor. Switching it to a low has no effect.
3. On my test board, I have a pull-up 33K resistor connected between pin 4 and pin 1. I have tried the above with and without this pull-up resistor and it has no effect.
4. All the other I/Os work fine.
5. Please advise what settings I am missing or if the 12F508 is no longer compatable
Here is the simple test program I am using:
__CONFIG _OSC_IntRC & _WDT_OFF & _CP_ON & _MCLRE_OFF
MAIN CODE 0x000
movwf OSCCAL ; update register with factory cal value
start movlw b'11101000' ; set GP0,GP1,GP2,GP4 as outputs
movlw b'11011111' ;Disable "TOCKl" at pin #5
Begin clrf GPIO ;Repeat ON-OFF action
Sequence BSF GPIO,0