f_12_16_r2r_dac.c

* Use 10 MHz crystal frequency. * Use Timer0 for ten millisecond looptime. * Blink "Alive" LED e

// For MCC18, this file uses the -Oi flag, which
// turns on integer promotions so that (ADRESH << 8) works.

#include "config.h"
#include "delay.h"

#include "jwb.h"

/*
 * program to generate square wave output on RB7..RB0 using
 *  R-2R resistor ladder and TMR2 interrupts
 */

// FUNCTION PROTOTYPES
int ReadAdcChannel(unsigned char c);

// GLOBAL VARIABLES AND STATIC DATA
volatile unsigned char    itmr, iamp;
unsigned char	idx;
#if defined(__18CXX)
rom
#endif
 const unsigned char sinetbl[] =  {127,133,139,146,152,158,164,170,  \
  176,181,187,192,198,203,208,212,217,221,225,229,233,236,239, \
  242,244,247,249,250,252,253,253,254,254,254,253,253,252,250, \
  249,247,244,242,239,236,233,229,225,221,217,212,208,203,198, \
  192,187,181,176,170,164,158,152,146,139,133,127,121,115,108, \
  102,96,90,84,78,73,67,62,56,51,46,42,37,33,29,25,21,18,15,12, \
  10,7,5,4,2,1,1,0,0,0,1,1,2,4,5,7,10,12,15,18,21,25,29,33,37, \
  42,46,51,56,62,67,73,78,84,90,96,102,108,115,121 };

#if defined(HI_TECH_C)
void interrupt pic_isr(void)
#endif
#if defined(__18CXX)
#pragma interrupt pic_isr
void pic_isr(void)
#endif
{
	unsigned char temp;

	if (TMR2IF) {
		temp = sinetbl[idx];		// get sine fcn value
		temp >>= iamp;				// reduce amplitude based on AN1 input
		PORTB = temp;				// write new DAC value
		TMR2IF = 0;					// clear IRQ flag
		PR2 = 250-itmr;				// change TMR2 period based on AN0 input
		idx++;						// increment ptr for next update
		idx &= 0x7F;				// ensure ptr is in range
	} // end if
} // end pic_isr

// use ADC to convert channel denoted by c and returns result in int
// NOTE: Assumes ADC is already on and proper ADC clk is selected
int ReadAdcChannel(unsigned char c) {
    unsigned char temp;

    temp = ADCON0 & 0xC1;	// get current ADCON0 (clearing CHS2:CHS0)
    ADCON0 = temp | ((c & 0x7)<<3);  // select the desired ADC channel
    DelayUs(20);              // wait 20us for ADC to get ready
    GODONE = 1;               // start ADC conversion,
    while(GODONE);            //   then wait for ADC to finish
    if ( ADFM )
      return ((ADRESH << 8) | ADRESL );
    else
      return ((ADRESH << 2) | (ADRESL>>6) );
} // end ReadAdcChannel

void main(void)
{
	int				temp;

	SET_AS_OUTPUT(TRISA, BIT1 | BIT2 | BIT3 | BIT5 | BIT6 | BIT7 );
	SET_AS_INPUT(TRISA, BIT0 | BIT1 | BIT3);

	PORTB = 0x00;
	SET_AS_OUTPUT(TRISB, BIT0 | BIT1 | BIT2 | BIT3 | BIT4 | BIT5 | BIT6 | BIT7 );

	// configure number of ADC channels and references (AN0+AN1+AN3+ no Vrefs)
	PCFG3=0; PCFG2=1; PCFG1=0; PCFG0=0;
	// set ADC conversion clock to internal ADC clock
	ADCS2=1; ADCS1=1; ADCS0=1;
	// select ADC channel 0
	CHS2=0; CHS1=0; CHS0=0;
	// set ADC results to be left justified (ADRESH has MSB)
	ADFM=0;
	// turn on ADC
	ADON=1;
	// wait before we kick off a conversion 	DelayUs(100);

	idx = 0; itmr = 0; iamp = 0;					// init ISR variables

	// configure TMR2 and turn it on
	PR2 = 250;										// setup IRQs every 250 cycles
	T2CON = 0x04;									// 1:1 post, 1:1 pre, turn on TMR2
	TMR2IF = 0;										// clear flag before enabling IRQ
	IPEN = 0; TMR2IE = 1; PEIE = 1; GIE = 1;		// enable TMR2 interrupts

	while(1) {
		temp = ReadAdcChannel(0);
		itmr = temp>>3;								// make itmr 0-127
		DelayMs(50);								// wait a long time

		temp = ReadAdcChannel(1);
		iamp = temp>>8;								// make iamp 0-3
		DelayMs(50);								// wait a long time
	} // end while
} // end main()

//for MCC18, place the interrupt vector goto
#if defined(__18CXX)
#if defined(HIGH_INTERRUPT)
#pragma code HighVector=HIGH_INTERRUPT
#else
#pragma code HighVector=0x0008  
#endif
void HighVector (void)
{
    _asm goto pic_isr _endasm
}
#pragma code
#endif