ad7703.c

高精度AD770程序

/*
 * ad7703.c
 *
 * AD7703
 *
 * 
 *
 *						陈真勇(SA01010010)
 *						[e-mail] or
 *						[e-mail]
 *						中国科学技术大学自动化系
 *						2002/6/12
 */

#include "type.h"
#include "delay.h"
#include "link.h"
#include "watchdog.h"

void selfcal()
{
	BYTE i;

	ADCS=1;
	ADCAL=1;
	delay10us();
					/* note: Self calibration last for at least 4 cycle clocks,
					and AD7703's main clock is 2M Hz. Our AT89C52 is 
					12 MHz,so we put 4 NOP instructions here. If frequency
					changed, you should change number of NOPs accordingly.*/
	ADCAL=0;
}

UINT read_ad()
{
	BYTE i=20;	/* 20 bits to be read */
	UINT mask=0x8000;
	UINT result=0;

	do{}while( ADDRDY );

	EA = 0;

	/*read first 16 bits of total 20 bits*/
	ADCS=1;
	ADCS=0;
	
	do{
		ADSCLK=1;/* data valid on rising edge */
	
		if(i>4 && ADSDATA){	/* max delay 75 ns before data valid. first check i>4*/
			result |= mask;
		}
		mask >>= 1;

		ADSCLK=0;/* data changed on falling_edge */
	}while(--i);

	ADCS=1;

	EA = 1;

	return result;
}

void init_ad7703()
{
	BYTE i;
	selfcal();/*self calibration*/
	/*we must wait for 3,500,000 clock cycles befor can access AD7703. It's
		about 2s long*/
	/* ????????????????????? */
	for(i=0;i<20;i++){
		/* TODO: you should clear watch dog while waiting.
			you should provide delay function that delay
			1 ms */
		clear_watchdog();
		delay(100);
	}
}