demo_16_2__.c

AVR单片机嵌入式系统原理与应用实践例码

/*****************************************************
File name           : demo_16_2.c
Chip type           : ATmega16
Program type        : Application
Clock frequency     : 4.000000 MHz
Memory model        : Small
External SRAM size  : 0
Data Stack size     : 256
*****************************************************/
#include <mega16.h>
	#ifndef __SLEEP_DEFINED__
	#define __SLEEP_DEFINED__
	.EQU __se_bit=0x40
	.EQU __sm_mask=0xB0
	.EQU __sm_powerdown=0x20
	.EQU __sm_powersave=0x30
	.EQU __sm_standby=0xA0
	.EQU __sm_ext_standby=0xB0
	.EQU __sm_adc_noise_red=0x10
	.SET power_ctrl_reg=mcucr
	#endif
#include <stdio.h>				// 使用CVAVR的标准 Input/Output 函数
#include <delay.h>				// 使用CVAVR的延时函数

#define EEPROM_BUS_ADDRESS 0xa0

#define SCL			DDRC.0
#define SDA			DDRA.0
#define SCL_Input   PINC.0
#define SDA_Input	PINA.0
#define SCL_Output  PORTC.0
#define SDA_Output  PORTA.0

#define SCL_Hight	SCL = 0
#define SCL_Low		SCL = 1
#define SDA_Hight	SDA = 0
#define SDA_Low		SDA = 1
#define I2C_Delay	delay_us(1)

void I2C_init(void)
{
    SCL_Output = 0;
    SDA_Output = 0;
    SCL_Low;
    SDA_Low;
}

//产生启动信号
unsigned char I2C_start(void)
{
  SDA_Hight;
  I2C_Delay;
  SCL_Hight;
  I2C_Delay;
  SDA_Low;
  I2C_Delay;
  SCL_Low;
  I2C_Delay;
  return 1;
}

//产生停止信号
void I2C_stop(void)
{
  SDA_Low;
  I2C_Delay;
  SCL_Hight;
  I2C_Delay;
  SDA_Hight;
  I2C_Delay;
}

//向总线写一字节,并返回有无应答
unsigned char I2C_write(unsigned char c)
{
  unsigned char i,ack = 1;
  for(i=0;i<8;i++)
  {
    if(c&0x80)
      SDA_Hight;
    else
      SDA_Low;
    SCL_Hight;
    I2C_Delay;
    SCL_Low;
    c<<=1;
    I2C_Delay;
  }
  SDA_Hight;
  I2C_Delay;
  SCL_Hight;
  I2C_Delay;
  if(SDA_Input)
    ack=0;     //失败
  SCL_Low;
  I2C_Delay;
  return ack;
}

//读一字节 ack: 1时应答，0时不应答
unsigned char I2C_read(unsigned char ack)
{
  unsigned char i,ret;
  SDA_Hight;
  for(i=0;i<8;i++)
  {
    I2C_Delay;
    SCL_Low;
    I2C_Delay;
    SCL_Hight;
    I2C_Delay;
    ret<<=1;
    if(SDA_Input)
      ret++;
  }
  SCL_Low;
  I2C_Delay;
  if(ack)      //非应答
    SDA_Low;
  else          //应答
    SDA_Hight;
  I2C_Delay;
  SCL_Hight;
  I2C_Delay;
  SCL_Low;
  I2C_Delay;
  return(ret);
}

// read a byte from the 24C256
unsigned char eeprom_read(unsigned int address)
{
    unsigned char data;
    I2C_start();						// 发起始信号
    I2C_write(EEPROM_BUS_ADDRESS);		// 发写从机写寻址字节
    I2C_write(address>>8);				// 发存储单元地址高字节
    I2C_write(address);					// 发存储单元地址低字节
    I2C_start();						// 发起始信号
    I2C_write(EEPROM_BUS_ADDRESS | 1);	// 发从机读寻址字节
    data=I2C_read(0);					// 读一个字节数据，返回NO ACK
    I2C_stop();						// 发停止信号
    return data;
}

// write a byte to the 24C256
void eeprom_write(unsigned int address, unsigned char data)
{
    I2C_start();						// 发起始信号
    I2C_write(EEPROM_BUS_ADDRESS);		// 发写从机写寻址字节
    I2C_write(address>>8);				// 发存储单元地址高字节
    I2C_write(address);					// 发存储单元地址低字节
    I2C_write(data);					// 写一个字节数据到24C256
    I2C_stop();						// 发停止信号
    delay_ms(10);			// 等待10ms，保证24C256内部写操作完成再进行新操作
}

void main(void)
{
    unsigned char i;
    UCSRA=0x00;		// USART initialization
    UCSRB=0x18;		// Communication Parameters: 8 Data, 1 Stop, No Parity
    UCSRC=0x86;		// USART Receiver: On，USART Transmitter: On
    UBRRH=0x00;		// USART Mode: Asynchronous	，USART Baud Rate: 9600
    UBRRL=0x19;
    //================================================
    I2C_init();		  // initialize the I2C bus
    eeprom_write(0x00aa,0x55);		// write the byte 55h at address 00AAh
    i = eeprom_read(0x00aa);		// read the byte from address 00AAh
    //================================================
    while (1)
    {
     	putchar(i);
       	delay_ms(250);
   	}
}