PIC Capture mode not triggering interrupt

Question

I'm trying to use the capture module on a PIC 16LF1827, but the ISR is never entered. I started with a basic falling-edge interrupt (worked), then added in the timer 1 configuration (still working), then disabled the IOC interrupt and configured/enabled the relevant CCP interrupt (ISR is never entered). The code is below: the commented section is the original basic IOC setup.

I've verified with the MPLab debugger that the ISR is not entered, and confirmed this by hooking it up to a logic analyzer and watching RB1.

#include "htc.h"

//config1
//internal osc, no wdt, use power-up timer, enable reset
//  no code protection, brown-out-reset enabled, clkout is gpio, 
//  internal-external switchover off, failsafe clock monitor off
__CONFIG(FOSC_INTOSC & WDTE_OFF & PWRTE_ON 
  & MCLRE_ON & CP_OFF & CPD_OFF & BOREN_ON 
  & CLKOUTEN_OFF & IESO_OFF & FCMEN_OFF);

//config2 (following MPLab's complaints when running debugger)
//low-voltage programming off, debug on, brown-out reset at 2.7 v
//  stack over/under flow triggers reset, no 4x pll, 
//  no flash write protection
__CONFIG(LVP_OFF & DEBUG_ON & BORV_27 
  & STVREN_ON & PLLEN_OFF & WRT_OFF);

void interrupt isr(void){
    //bounce pin 1
    LATB ^= 0b10;
    LATB ^= 0b10;
    if(IOCIF && IOCBF0){
        IOCBF0 = 0;
        IOCIF = 0; 
    }
    if (CCP1IF){
        CCP1IF = 0;
    }
}

void main(void){
    //configure internal oscillator: 
    //PLL = 0, source = from config 1, frequency = 4 mhz 
    //0b0: SPLLEN_OFF
    OSCCONbits.SPLLEN = 0b0;
    //0b00: use config word 1
    OSCCONbits.SCS = 0b00;
    //0b1101: 4 mhz frequency
    OSCCONbits.IRCF = 0b1101;

    //configure peripherals
    //PORT A: LEDs (output), digital
    TRISA = 0x00;
    ANSELA = 0;
    //PORT B: digital, 0 = input, 1 = output, rest don't care
    TRISB = 0b11111101;
    ANSELB = 0;

    //configure timer 1 (not needed for basic IOC)
    //source = instruction clock, prescale = 1:1, disable LP osc, do synchronize (DC)
    //0b00: instruction clock
    T1CONbits.TMR1CS = 0b00;
    //0b00: 1:1
    T1CONbits.T1CKPS = 0b00;
    //0b0: lp osc off
    T1OSCEN = 0b0;
    //0b0: synch (ignored)
    nT1SYNC = 0b0;

    //interrupts
    /*
    //IOC enabled on falling edge for port B 0
    IOCBN0 = 0b00000001;
    IOCIE = 1;
    */

    //Capture on falling edge for port B 0
    //notes in 23.1 of DS: disable interrupt, set operating mode, clear flag, enable interrupt
    CCP1IE = 0b0;
    //0b100: every falling edge
    CCP1CONbits.CCP1M = 0b100;
    CCP1IF = 0b0;
    CCP1IE = 0b1;
    //enable peripheral interrupts, global interrupts
    PEIE = 1;
    GIE = 1;

    //start timer 1
    TMR1ON = 1;
    while(1){
        //Toggle led 0
        LATA ^= 0b1;
    }
}

I'm using the HI-TECH C compiler (lite), running in MPLab.

Any suggestions would be greatly appreciated. My apologies if I butcher terminology, this is my first project on a PIC.

Doug, while StackOverflow is really good, be sure to mirror you question on the specialized PIC forums: HI-TECH forum forum.htsoft.com/all/postlist.php/Cat/0/Board/pic , Microchip forum microchip.com/forums . — Nick Alexeev

spade78 spade78 · Accepted Answer · 2011-03-28T23:13:03

~~Your setting for TRISB1 is as an output. According to the datasheet, the capture pin needs to be configured as an input. For the GPIO pins, setting the TRIS bit a 0 is an output, 1 is for an input.~~

EDIT: Forgive the initial stupid answer as I didn't realize you were using PORTB1 as a GPIO indicator for your scope.

So initially you used PORTB0 as your capture pin correct (using IOC)? The capture module uses a different GPIO port for its input (PORTB3 for CCP1). Did you move the connection to PORTB3 for your capture source?

EDIT: After some more looking through the PIC datasheet I noticed that CCP1's GPIO pin can be moved from PORTB3 to PORTB0 but I don't see any reference to how you set the APFCON0.CCP1SEL bit. That would be something else to check.

PIC Capture mode not triggering interrupt

1 Answers