pwm_2.c

Low End Microchip PICs C函数

// Program PWM_3.C
//
// Varies PWM duty using potentiometer on A/D Ch0 and outputs
// the value of "duty" to LCD.
//
// Uses 10-bit PWM.  The period is 1/256 us.
//
// copyright, Peter H. Anderson, Baltimore, MD, Dec, '00

#case

#device PIC16F877 *=16 ICD=TRUE

#include <defs_877.h>
#include <lcd_out.h> // LCD and delay routines

main()
{

   struct DUTY
   {
       byte hi8;  // high 8 bits of duty cycle
       byte lo2;  // low 2 bits in the highest two bits
   };

   struct DUTY duty;
   long duty_l;


   pcfg3 = 0; pcfg2 = 1; pcfg1 = 0; pcfg0 = 0;
   // config A/D for 3/0

   lcd_init();

   // set up A/D converter
   adfm = 0;   // right justified -
               // high 8 bits in ADRESH, lowest two bits in high bits of ADRESL
   adcs1 = 1; adcs0 = 1; // internal RC

   adon=1;  // turn on the A/D
   chs2=0;  chs1=0;   chs0=0;

   delay_10us(10);      // a brief delay

   // Configure CCP1
   duty.hi8 = 0x00;
   duty.lo2 = 0x00;

   PR2 = 0xff;    // period set to max of 256 * 4 usecs  - about 1 kHz

   CCPR1L = duty.hi8;      // duty initially set to zero
   ccp1x = 0;  ccp1y = 0;  // low 8-bits of duty

   // configure CCP1 for PWM operation
   ccp1m3 = 1;  ccp1m2 = 1;

   // Timer 2 post scale set to 1:1
   toutps3 = 0;  toutps2 = 0; toutps1 = 0; toutps0 = 0;

   // Timer 2 prescale set to 1:1
   t2ckps1 = 0; t2ckps0 = 0;

   tmr2on = 1; // turn on timer #2

   portc2 = 0;
   trisc2 = 0; // make PORTC.2 an output 0

   while(1)
   {
      adgo = 1;
      while(adgo)    ;  // poll adgo until zero
      duty.hi8 = ADRESH;
      duty.lo2 = ADRESL;
      CCPR1L = duty.hi8;      // high 8-bits

      ccp1x = 0;  ccp1y =0;   // low 2 bits
      if (duty.lo2 & 0x80)
      {
          ccp1x = 1;
      }
      if (duty.lo2 & 0x40)
      {
          ccp1y = 1;
      }
      lcd_cursor_pos(0, 0);
      duty_l = ((long) (duty.hi8)) * 4 + (duty.lo2 >> 6);
      printf(lcd_char, "%lx", duty_l);
      delay_ms(25);
   }
}

#include <lcd_out.c>