EX_PWM.C
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/////////////////////////////////////////////////////////////////////////
//// EX_PWM.C ////
//// ////
//// This program will show how to use the built in PIC PWM. ////
//// The program takes an analog input and uses the digital ////
//// value to set the duty cycle. The frequency is set by ////
//// the user over the RS-232. ////
//// ////
//// Configure the CCS prototype card as follows: ////
//// Connect a scope to pin 3 (C2) ////
//// Connect 9 to 15 (pot) ////
//// See additional connections below. ////
//// ////
//// This example will work with the PCM and PCH compilers. The ////
//// following conditional compilation lines are used to include a ////
//// valid device for each compiler. Change the device, clock and ////
//// RS232 pins for your hardware if needed. ////
/////////////////////////////////////////////////////////////////////////
//// (C) Copyright 1996,2001 Custom Computer Services ////
//// This source code may only be used by licensed users of the CCS ////
//// C compiler. This source code may only be distributed to other ////
//// licensed users of the CCS C compiler. No other use, ////
//// reproduction or distribution is permitted without written ////
//// permission. Derivative programs created using this software ////
//// in object code form are not restricted in any way. ////
/////////////////////////////////////////////////////////////////////////
#if defined(__PCM__)
#include <16c74.h>
#fuses HS,NOWDT,NOPROTECT
#use delay(clock=10000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, BRGH1OK) // Jumpers: 8 to 11, 7 to 12
#elif defined(__PCH__)
#include <18c452.h>
#fuses HS,NOPROTECT
#use delay(clock=10000000)
#use rs232(baud=9600, xmit=PIN_C6, rcv=PIN_C7, BRGH1OK) // Jumpers: 8 to 11, 7 to 12
#endif
main() {
char selection;
byte value;
printf("\r\nFrequency:\r\n");
printf(" 1) 19.5 khz\r\n");
printf(" 2) 4.9 khz\r\n");
printf(" 3) 1.2 khz\r\n");
do {
selection=getc();
} while((selection<'1')||(selection>'3'));
setup_ccp1(CCP_PWM); // Configure CCP1 as a PWM
// The cycle time will be (1/clock)*4*t2div*(period+1)
// In this program clock=10000000 and period=127 (below)
// For the three possible selections the cycle time is:
// (1/10000000)*4*1*128 = 51.2 us or 19.5 khz
// (1/10000000)*4*4*128 = 204.8 us or 4.9 khz
// (1/10000000)*4*16*128= 819.2 us or 1.2 khz
switch(selection) {
case '1' : setup_timer_2(T2_DIV_BY_1, 127, 1);
break;
case '2' : setup_timer_2(T2_DIV_BY_4, 127, 1);
break;
case '3' : setup_timer_2(T2_DIV_BY_16, 127, 1);
break;
}
setup_port_a(ALL_ANALOG);
setup_adc(adc_clock_internal);
set_adc_channel( 0 );
printf("%c\r\n",selection);
while( TRUE ) {
value=read_adc();
printf("%2X\r",value);
set_pwm1_duty(value); // This sets the time the pulse is
// high each cycle. We use the A/D
// input to make a easy demo.
// the high time will be:
// if value is LONG INT:
// value*(1/clock)*t2div
// if value is INT:
// value*4*(1/clock)*t2div
// for example a value of 30 and t2div
// of 1 the high time is 12us
// WARNING: A value to high or low will
// prevent the output from
// changing.
}
}
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