Short C code for PIC16F627A builds but won't run properly

[ocset]

Hello,
Our short  C   code builds but won’t run properly. (please find it attached)     
(the output  RB5, never goes high, even though the pulse train is definitely getting to the input pin RA2)
It is written in XC8 C in MPLAB.
The microcontroller is PIC16F627A
Do you know why it doesn’t work as it should?         

Code: [Select]

//This code simply  has an input "looking"
//at a train of pulses.
//When one of the pulses goes low, a delay is done....
//and then an output is taken high.

// CONFIG
#pragma config FOSC = INTOSCIO  // Oscillator Selection bits (INTOSC oscillator: I/O function on RA6/OSC2/CLKOUT pin, I/O function on RA7/OSC1/CLKIN)
#pragma config WDTE = OFF       // Watchdog Timer Enable bit (WDT disabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = OFF      // RA5/MCLR/VPP Pin Function Select bit (RA5/MCLR/VPP pin function is digital input, MCLR internally tied to VDD)
#pragma config BOREN = OFF      // Brown-out Detect Enable bit (BOD disabled)
#pragma config LVP = OFF        // Low-Voltage Programming Enable bit (RB4/PGM pin has digital I/O function, HV on MCLR must be used for programming)
#pragma config CPD = OFF        // Data EE Memory Code Protection bit (Data memory code protection off)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)

// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.

#define  _XTAL_FREQ 4000000

#include <xc.h>
#include <stdint.h>



    uint8_t   count;
    uint8_t   count1;
    uint8_t   count2;

void main(void) {
   
    //Setup ports
    //    TRISA = 0b 1011 1100;   //ADC INS
    //    TRISB = 0b 00000001;    //ZCD & DALIRX..really 0x09
   
    TRISA = 0xBC;
    TRISB = 0x01;

                RA0 = 0;    //NC
                RA1 = 0;    //NC
                //RA2 = 0;    //ZERO X   ..input
                //RA3 = 0;    //on/off ..input
                //RA4 = 0;    //select zapper ..input
                //RA5 = 0;    //RA5 ..MCLR ..input
                RA6 = 0;    //RA6 ..LED failure ..output
                //RA7 = 0;    //failure ..input
               
                //RB0 = 0;    //SELECT OAMP ..INPUT
                RB1 = 0;    //LED ..ZAPPER ..OUTPUT
                RB2 = 0;    //LED OAMP ..OUTPUT
                RB3 = 0;    //NC ..OUTPUT
                RB4 = 0;    //ZAPPER SWITCH ..OUTPUT
                RB5 = 0;    //AC SWITCH ..OUTPUT
                RB6 = 0;    //PGC ...OUTPUT
                RB7 = 0;    //PGD  ..OUTPUT
 

        INTCON = 0x00;
        //OPTION_REG = 0b 10000111
        OPTION_REG = 0x87;
        //VRCON = 0b00;
        VRCON = 0x00;
        CMCON = 0x07;
       
        while (RA2 == 0);
        while (RA2 ==1);
       
        //At this point the pulse has just gone low
       
        __delay_ms(3);   //delay to get to the mains peak
        __delay_us(600);
       
        RB5 = 1;
        __delay_ms(1);
        RB5 = 0;
       
        while(1){;}
           
       
    return;
}


[rstofer]

How are you capturing that single 1 ms pulse?  It seems to me that it could be over and done with in a blink.
I would reorganize the code such that I got a continuous output every time I had a transition on the input.

[Howardlong]

It looks like it runs fine here, using the AC244053 AC162053 debug header as I didn't have a production chip. I also have a non-A PIC16F628 production chip (a bit more flash & RAM than the 627, but the same datasheet) and it works fine with that too.

A nice 970us high pulse on RB5 when I take RA2 high, good enough for the girls I go out with.

Edit: corrected header part number.

[ocset]

Thanks,
We are looking at it with a scope on sample/hold

[AndyC_772]

This isn't just the usual ANSEL trap, is it? Do GPIO pins come up in analogue mode on this device?

[JPortici]

No, that's taken care of by CMCON

I don't like to read pins this way.. it should work but i always ran into problems.
i like to sample the PORT and then operate on the sampled value.

Code: [Select]

uint8_t porta_buf;

[..]
porta_buf = PORTA;

while(!(porta_buf & (1 << 2))) {
  // same as while(RA2 == 0), gets optimized at compile time
  porta_buf = PORTA;
}

while((porta_buf & (1 << 2))) {
  //same as while(RA2 == 1)
  porta_buf = PORTA;
}

[..]


[@rt]

Have you flashed an LED to prove the pic is clocking?

You have ms delays, so plant of time to shadow your port registers as above yes,
and an easy program to debug the old fashioned way.
You could insert LED outputs inside both of those while loops,
change the first while to an IF, and put the second while loop inside it, etc.

[mikerj]

I don't like to read pins this way.. it should work but i always ran into problems.

Agreed, the code that the OP posted is risking the usual PIC Read-Modify-Write problems during initialisation where he is setting multiple pins on the same port consecutively.  Unless the PIC has a latch register (LATx) then this should be avoided, by writing the entire PORT initialisation value in one go in this case, or by using a shadow register for RMW operations.

However this shouldn't normally be a problem for the output pulse since there is a significant delay between setting and clearing the pin.