Now to some coding! I'm using Microchip's free IDE (MPLAB X) and the free version of their C compiler XC8.
As a first step I always like to code the basic 'blinking LED' in a new PIC project. I use interrupts instead of delays because in addition to having a visual indication that the PIC is alive, I also use the same interrupt routine to handle any delays I may need down the road. XC8 does have built-in delay functions however, XC8 delay functions actually inserts NOP instructions into the code and you can't pass a variable into the XC8 delay function. You need to know all your static only delays ahead of time! Not very robust or efficient, so I use an interrupt routine to handle all delays instead of the built in XC8 functions. In addition to this basic 'heartbeat' I also configured two CCP peripherals as PWM channels for the control of the two drive motors.
First we configure the PIC 16F1829 fuses:
/* configuration_bits.c */
#include <xc.h> /* XC8 General Include File */
#include <xc.h>
// #pragma config statements should precede project file includes.
// Use project enums instead of #define for ON and OFF.
// CONFIG1
#pragma config FOSC = INTOSC // Oscillator Selection (INTOSC oscillator: I/O function on CLKIN pin)
#pragma config WDTE = OFF // Watchdog Timer Enable (WDT disabled)
#pragma config PWRTE = OFF // Power-up Timer Enable (PWRT disabled)
#pragma config MCLRE = ON // MCLR Pin Function Select (MCLR/VPP pin function is MCLR)
#pragma config CP = OFF // Flash Program Memory Code Protection (Program memory code protection is disabled)
#pragma config CPD = OFF // Data Memory Code Protection (Data memory code protection is disabled)
#pragma config BOREN = ON // Brown-out Reset Enable (Brown-out Reset enabled)
#pragma config CLKOUTEN = OFF // Clock Out Enable (CLKOUT function is disabled. I/O or oscillator function on the CLKOUT pin)
#pragma config IESO = ON // Internal/External Switchover (Internal/External Switchover mode is enabled)
#pragma config FCMEN = ON // Fail-Safe Clock Monitor Enable (Fail-Safe Clock Monitor is enabled)
// CONFIG2
#pragma config WRT = OFF // Flash Memory Self-Write Protection (Write protection off)
#pragma config PLLEN = ON // PLL Enable (4x PLL enabled)
#pragma config STVREN = ON // Stack Overflow/Underflow Reset Enable (Stack Overflow or Underflow will cause a Reset)
#pragma config BORV = LO // Brown-out Reset Voltage Selection (Brown-out Reset Voltage (Vbor), low trip point selected.)
#pragma config LVP = ON // Low-Voltage Programming Enable (Low-voltage programming enabled)
Now the system config:
/* system.h */
#define SYS_FREQ 1600000L
#define FCY SYS_FREQ/4
/******************************************************************************/
/* System Function Prototypes */
/******************************************************************************/
void ConfigureOscillator(void); /* Handles clock switching/osc initialization */
...and
/* system.c */
#include <xc.h> /* XC8 General Include File */
#include <stdint.h> /* For uint8_t definition */
#include <stdbool.h> /* For true/false definition */
#include "system.h"
void ConfigureOscillator(void)
{
OSCCON=0b01111010;
while (!HFIOFS) continue;// wait for stable osc
}
The code below contains the configuration of both the CCP and Timer 2 for use as a 1ms interrupt timer.
/* user.c */
#include <xc.h> /* XC8 General Include File */
#include <stdint.h> /* For uint8_t definition */
#include <stdbool.h> /* For true/false definition */
#include "user.h"
void InitApp(void)
{
/* Heartbeat config */
TRISAbits.TRISA5 = 0; // Heartbeat LED
TMR2=0;// clear TMR2
T2CON = 0b00000110;//post 0, timer on, pre 16
PR2=0xF9; // sets up timer2 for 1ms interrupts
/* PWM Left config */
TRISCbits.TRISC6 = 0; // Left PWM output
T4CON = 0b00000110;//post 0, timer on, pre 16
PR4 = 0xF9; // 1000 Hz PWM freq
CCP4CON = 0x3C;// PWM mode
CCPR4H = 0;
CCPR4L = 0x3E; // Duty cycle count 1% = 0x9 to 100% = 0xF9
CCPTMRS = 0x40; // use Timer 4
/* PWM Right config */
TRISAbits.TRISA2 = 0; // Right PWM output
T6CON = 0b00000110;//post 0, timer on, pre 16
PR6 = 0xF9; // 1000 Hz PWM freq
CCP3CON = 0x1C; // PWM mode
CCPR3H = 0;
CCPR3L = 0x7C; // Duty cycle count 1% = 0x9 to 100% = 0xF9
CCPTMRS = 0x20; // use Timer 6
/* Enable interrupts */
PIR1bits.TMR2IF=0; // clear TMR2 interrupt flag
PIE1bits.TMR2IE=1;//enable TMR2 interrupts
INTCONbits.PEIE=1;//enable Peripheral interrupts
INTCONbits.GIE=1;// enable global interrupts
}
void msDelay(unsigned int d){
// load up the msec delay variable
ms_delay=d;
// loop execution here until msec delay completes via 1 ms interrupts
while(ms_delay)continue;
}
We will be manipulating the CCPR3L and CCPR4L registers to vary the duty cycles for the two motors. For now however, they are hard-coded to generate a 25% duty cycle on the Left motor and 50% on the right motor as a test. Note the msDelay function I wrote to execute any delays needed. It simply sets a global variable with the amount of msecs needed and the 1ms interrupt routine decrements that variable until it reaches zero! The delay routine just loops checking for that variable to reach zero.
The O'scope shot below shows the two outputs from the PIC with the top trace being the Left and the bottom trace being the Right.
The interrupt routine:
/* interrupts.c */
#include <xc.h> /* XC8 General Include File */
#include <stdint.h> /* For uint8_t definition */
#include <stdbool.h> /* For true/false definition */
#include "user.h"
void interrupt isr(void)
{
INTCONbits.GIE=0;// disable all interrupts
/* Determine which flag generated the interrupt */
if(PIR1bits.TMR2IF)// 1ms interrupt via Timer 2
{
if(hb_count++>500)// if counted 500ms
{
LED = ~LED; // toggle the 'heartbeat' LED
hb_count=0; // and reset the count to 0
}
if (ms_delay){ // if msec delay variable is not zero
ms_delay--; // decrement the delay
}
PIR1bits.TMR2IF=0; // clear Timer 2 interrupt flag
}
else
{
/* Unhandled interrupts */
}
INTCONbits.GIE=1;// enable global interrupts
}
General definitions:
/* user.h */
#define _XTAL_FREQ 16000000 // Fosc frequency for _delay() library
#define LED LATAbits.LATA5
/******************************************************************************/
/* User Function Prototypes */
/******************************************************************************/
void msDelay(unsigned int d);
void InitApp(void); /* I/O and Peripheral Initialization */
/* global variables */
unsigned int hb_count=0;// Heartbeat counter
unsigned long ms_delay=0;
The main routine is a bit bare since not much is going on yet!
/* main.c */
#include <xc.h> /* XC8 General Include File */
#include <stdint.h> /* For uint8_t definition */
#include <stdbool.h> /* For true/false definition */
#include "system.h" /* System funct/params, like osc/peripheral config */
#include "user.h" /* User funct/params, such as InitApp */
void main(void)
{
/* Configure the oscillator for the device */
ConfigureOscillator();
/* Initialize I/O and Peripherals for application */
InitApp();
while(1)
{
}
}
