8574.c

PCF8574 Remote 8-bit I/O expander for I2C-bus IO扩展芯片测试程序

#include <reg52.h>
#include <stdio.h>

sbit SCL=P3^7;
sbit SDA=P3^6;

typedef unsigned char byte;

byte in_patt(byte device);
void out_patt(byte device, byte dirs, byte patt);
void out_byte(byte o_byte);
byte in_byte(void);
byte nack(void);
void start(void);
void stop(void);

void delay(int a)
{
 	for (;a>0;a--)
 		;
}

void DelayMs(unsigned char t)
{
	unsigned char i;
    if(t>0)
    {
 		for(i=0;i<=10;i++)
  			;
		t--;
	}
}

void main(void)
{
	byte i_patt, device;
	byte dirs = 0x80; /* define most significant bit as an input */

	device = 0x00; /* determined by strapping of A2, A1, A0 */
	out_patt(device, dirs, 0xff);
	/* initialize all outputs to logic one */
	while(1)
	{
		i_patt=in_patt(device); /* fetch from 8574 */
		if ((i_patt && 0x80)==0) /* if switch at zero, flash LED */
		{
			out_patt(device, dirs, 0x00); /* LED on */
			DelayMs(250);
			out_patt(device, dirs, 0x01); /* LED off */
			DelayMs(250);
		}
		else
		{
			out_patt(device, dirs, 0x01); /* turn LED off */
		}
	}
}

byte in_patt(byte device) 
/* fetches byte from 8574 at specified addresss */
{
	byte o_byte, i_patt;
	start();
	o_byte=0x40 | (device << 1) | 0x01;
	out_byte(o_byte);
	nack();
	i_patt=in_byte();
	stop();
	return(i_patt);
}

void out_patt(byte device, byte dirs, byte patt)
/* outputs specified pattern on specified 8574. Note that
** inputs specified by "dirs" are maintained at a logic one */
{
	byte o_byte;
	start();
	o_byte=0x40 | (device << 1);
	out_byte(o_byte);
	nack();
	o_byte = patt | dirs;
	out_byte(o_byte);
	nack();
	stop();
}

void out_byte(byte o_byte)
/* shift out byte, beginning with most significant bit */
{
	int n;
	for(n=7; n>=0; n--)
	{ /* note SCL is low during transitions on SDA */
		if (((o_byte >>n) & 0x01) == 0)
		{
			SDA=0;
		}
		else
		{
			SDA=1;
		}
		delay(4);
		SCL=1;
		delay(4);
		SCL=0;
		delay(4);
	}
}

byte in_byte(void)
/* fetch byte, most significant byte first */
{
	byte i_byte=0x00;
	int n;

	SDA=1;
	delay(4);
	for (n=0; n<8; n++)
	{
		SCL=1;
		delay(4);
		i_byte=(i_byte << 1) | SDA;
		delay(4);
		SCL=0;
	}
	return(i_byte);
}

byte nack(void)
{
	byte ack_bit;
	SDA=1;
	delay(4);
	SCL=1;
	delay(4);
	if (SDA==0)
	{
		ack_bit=0;
	}
	else
	{
		ack_bit=1;
	}
	SCL=0;
	delay(4);
	return(ack_bit);
}

void start(void)
/* bring SDA high to low while SCL is high */
{
	SDA=1;
	delay(4);
	SCL=1;
	delay(4);
	SDA=0;
	delay(4);
	SCL=0;
	delay(4);
}

void stop(void)
/* bring SDA low to high while SCL is high */
{
	SDA=0;
	delay(4);
	SCL=1;
	delay(4);
	SDA=1;
	delay(4);
	SCL=0;
	delay(4);
}