在单片机应用中,I2C(I方C)总线一种简单,双向的二线制同步串行总线,它只需要两根串行线,脉冲线,就可以在总线与连接的器件之间传送信息, 它不外乎有以下几个特点:
a.每个连接到总线上的器件都可以进行唯一的寻址,还可建立起简单的主从关系,主器件既可作为发送器,也可作为接收器.
b.它带竞争电路和仲裁电路,可以接收多个主器件发送的数据,而这些数据不会产混乱.
c.同步脉冲可以允许器件可以通过总线以不同的波特率进行通信.
d.因为只有两根线,连接简单,方便.
对于MCS51系列来讲,内部并没I2C总线接口，在这种情况下,可以采用软件模拟的方法来写出I2C总线的操作,下面我的程序就在开始处定义哪个引脚作为数据线SDA,哪个引脚作为脉冲线,请看我的程序(C51写的,总共有8个函数来模拟I2C总线):
Common.h File
#pragma LA DB SB OE CD OT(SPEED,6)
//LA indicate LARGE Compling Mode-All local and global variables are located in external-ram.
//DB indicate DEBUG
//SB indicate SYMBOL
//OE indicate OBJECTEXTEND
//CD indicate CODE //Generate ASM Code
//OT indicate OPTIMIZATION
#include <stdio.h>
#include <reg51.h>
#include <intrins.h>
#include <stdlib.h>
#pragma REGPARMS
#pragma SAVE
#define BOOL bit
#define BYTE unsigned char
#define UINT unsigned int
#define ULONG unsigned long
#define HIGH 1
#define LOW 0
#define TRUE 1
#define FALSE 0
#define MAXLONGS 2147483647
#define MINLONGS -2147483648
#define MAXINTS 32767
#define MININTS -32768
#define MAXLONGU 4294967295
#define MAXINTU 65535
#define BLOCKLOW 0x0000 //The start-address in AT24C64 is 0x0000
#define BLOCKSIZE 0x20 //Each block is 32 bytes
#define BLOCKNUM 0xC8 //At best 200,Only Save the newest 200 records.
#define BLOCKHIGH 0x18FF//The end-address in AT24C64 is 0x18FF
#define OSC 24000000 //Osillcator Frequency
#define BAUDRATE 9600
#define OTV 256-OSC/12/BAUDRATE/32 //character O represents Obtain,character T represents Timer,character V represents Value
//IMPORTANT ANNOUNCEMENT:I use a word 0x1FFC,0x1FFD to save the next block's address and 0x1FFE,0x1FFF to save the block's no.
sbit GUN=0x85;//PIN P05
sbit SCL=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit SDA=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit SHKL=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit SHKH=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit KH0=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit KH1=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
sbit KH2=0xFF; //Undefined bit-address,which will be defined in function:DEFI2C
extern void DEFI2C(char *name) //To define which pin is SDA and which pin is SCL
extern void I2CInit() //Initialization For I2C Bus
extern void I2CStart() //Start I2C Bus
extern void I2CStop(); //Stop I2C Bus
extern bit I2CClock(); //return SDA while SCL is HIGH
extern void I2CDelay(); //Delay
extern void I2CAck(); //Answer
extern bit I2CSend(BYTE I2CData);//Send data with I2C Bus
extern BYTE I2CReceive(); //Receive data
Common.c
void DEFI2C(char *name)
{
//Todo:add your codes here....
//Announcement:If you question me why use the function DEFI2C?
//Well,the function will be used to define which PIN is SCL and which PIN is SDA,especially there are more than 1 I2C
//equipment in your circuit.In this sitiuation,we write a function for defining I2C Bus named DEFI2C....
}
void I2CStart()
{
SCL=HIGH;
I2CDelay();
SDA=LOW;
I2CDelay();
SCL=LOW;
I2CDelay();
}
void I2CStop()
{
SDA=LOW;
I2CDelay();
SCL=HIGH;
I2CDelay();
SDA=HIGH;
I2CDelay();
SCL=LOW;
I2CDelay();
}
void I2CInit()
{
SCL=LOW;
I2CStop();
}
bit I2CClock() //return SDA while SCL is HIGH
{
bit sample;
SCL=HIGH;
I2CDelay();
sample=SDA;
SCL=LOW;
I2CDelay();
return sample;
}
bit I2CSend(BYTE I2CData)
{
BYTE i;
for(i=0;i<8;i++)
{
SDA=(bit)(((I2CData) & 0x80) / 0x80) ;
I2CData=I2CData << 1;
I2CClock();
}
SDA=HIGH;
return (~I2CClock());
}
void I2CAck()
{
SDA=LOW;
I2CClock();
SDA=HIGH;
}
void I2CDelay()
{
BYTE ll;
for(ll=0;ll<100;ll++)
{
;
}
}
BYTE I2CReceive()
{
BYTE I2CData=0;
BYTE kk;
for(kk=0;kk<8;kk++)
{
I2CData*=2;
if(I2CClock())
{
I2CData++;
}
}
return I2CData;
}
上面的代码是用软件来模拟I2C总线,在对特定I2C器件进行操作时,一定要和该器件的时序对应起来才可以,本人从事单片机开发不久，上述程序是去年在北京时写的,如有错误还请各位硬件大侠,前辈给予指教.
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