Simulating IIC Bus Timing Based on 51 Single-Chip Microcomputer

Recently, I need to use IIC bus operation when using the light measurement module BH1750FVI, so I spent some time to learn it and basically understood it. So, I used the IO port of 51 to simulate the bus timing and correctly operate a series of modules that need to be accessed by IIC bus. I originally wanted to write an article to briefly introduce my understanding of IIC bus, but I found that I didn’t have time, so I will do it later. Today I will only give a sample program, which can work well on my 51 single-chip computer system. iic.h lists all the operation functions of IIC bus. The source code is given below:

//iic.h - implementation related header file

//Girls Don't Cry 2013-01-18

#ifndef __IIC_H__

#define __IIC_H__

void iic_start(void);

void iic_stop(void);

bit iic_get_ack(void);

void iic_write_byte(uchar dat);

uchar iic_read_byte(void);

void iic_send_ack(bit ack);

#endif//!__IIC_H__

//IIC bus simulation implementation file

//Girls Don't Cry 22:11 2013-1-18

#include "common.h"

#include "iic.h"

sbit SDA = P1^2;

sbit SCL = P1^0;

//Generate START signal

void iic_start(void)

{

    SDA = 1; //need to be set before SCL

    SCL = 1; //Hardware enters SDA detection state

    delay_us(5); //Delay at least 4.7us

    SDA = 0; //SDA changes from 1->0, generating a start signal

    delay_us(5); //delay at least 4us

    SCL = 0; //SCL becomes invalid

}

//Generate STOP signal

void iic_stop(void)

{

    SDA = 0; // pull low before SCL

    SCL = 1; //Hardware enters SDA detection state

    delay_us(5); //Delay at least 4us

    SDA = 1; //SDA changes from 0->1, generating an end signal

    delay_us(5); //Delay at least 4.7us

}

//Write 1 byte to the IIC bus

void iic_write_byte(uchar dat)

{

    uchar loop = 8; //Must be one byte

    while(loop--){

        SDA = dat&0x80; //Write bit by bit starting from MSB

        SCL = 1;

        delay_us(5); //delay at least 4us

        SCL = 0;

        dat <<= 1; //Move from low to high

        delay_us(5);

    }

}

//Read 1 byte from the IIC bus

uchar iic_read_byte(void)

{

    uchar loop = 8; //Must be one byte

    uchar ret = 0;

    while(loop--){

        SDA = 1; //8051 internal resistor pull-up

        SCL = 1;

        delay_us(5); //delay at least 4us

        ret <<= 1;

        ret |= SDA; //read 1 bit

        SCL = 0 ;

        delay_us(5);

    }

    return ret;

}

//Send response code from master to slave

//0-ACK,1-NAK

void iic_send_ack(bit ack)

{

    SDA = ack; //Generate response level

    SCL = 1; //Send response signal

    delay_us(5); //delay at least 4us

    SCL = 0; //Maintain the response signal during the whole period

}

//Get the response code from slave to master

bit iic_get_ack(void)

{

    bit ret; // used to receive the return value

    SDA = 1; //Resistor pull-up, enter read (8051)

    SCL = 1; //Enter response detection

    delay_us(5); //Delay at least 4us

    ret = SDA; //Save the response signal

    SCL = 0;

    return ret;

}

　　The above code gives all the IIC bus programs.

　　Functions implemented in common.h and related definitions