I familiarising myself with MPLAB X IDE and staring development with C using a Microchip PIC 12F617.
I have a simple program (copied from elsewhere) to flash a LED: on for 1 second then off for 1 second. It all works but I my calculation of the delay does not match 1 second. Anybody able to tell me where I am going wrong?
Internal osc is selected @ 8 MHz
clock to TMR2 is FOSC / 4 is 2 MHz
PR2 default to 255 so interrupt at 2 MHz / 255 is 7843 Hz
TMR2 prescale = 1; postscale set to 16; is 490 Hz
Loop counts 675 is 0.726 Hz so LED should be on/off for 1.38 seconds, yet it isn't
Taking into account time for executing instructions the led on/off should be even longer.
what am I missing?
/*
* File: main.c
* Author: user2439830
* Target: PIC12F617
* Compiler: XC8 v2.05
*
* PIC12F617
* +------v------+
* 5v0 ->:1 VDD VSS 8:<- GND
* <>:2 GP5 GP0 7:<> PGD
* <>:3 GP4 GP1 6:<> PGC
* VPP ->:4 GP3 GP2 5:<>
* +-------------+
* DIP-8
*
* Created on May 20, 2020, 5:51 PM
*/
#pragma config FOSC = INTOSCIO // Oscillator Selection bits (INTOSCIO oscillator: I/O function on RA4/AN3/T1G/OSC2/CLKOUT, I/O function on RA5/T1CKI/OSC1/CLKIN)
#pragma config WDTE = ON // Watchdog Timer Enable bit (WDT enabled)
#pragma config PWRTE = OFF // Power-up Timer Enable bit (PWRT disabled)
#pragma config MCLRE = ON // MCLR Pin Function Select bit (MCLR pin is MCLR function and weak internal pull-up is enabled)
#pragma config CP = OFF // Code Protection bit (Program memory is not code protected)
#pragma config IOSCFS = 8MHZ // Internal Oscillator Frequency Select (8 MHz)
#pragma config BOREN = ON // Brown-out Reset Selection bits (BOR enabled)
#pragma config WRT = OFF // Flash Program Memory Self Write Enable bits (Write protection off)
#include <xc.h>
void t2delay( void );
void main(void)
{
// Note: TRISIO = TRISA; IO direction register
TRISIO = 0; // 0 set corresponding pin in GPIO to output
// 76543210
T2CON = 0b01111000; // postscale=16, prescale=1, timer off
T2CON |= ( 1 << 2 ); //timer2 on TMR2ON set to 1
while (1)
{
// Note: GPIO = PORTA
GPIO = 255;
t2delay();
GPIO = 0;
t2delay();
}
return;
}
// TMR2IF set to when when TMR2 == PR2 (set to 255 on reset)
void t2delay( void )
{
unsigned int i;
for( i = 0; i < 675; i++)
{
while( !TMR2IF );
TMR2IF = 0;
}
}
