AD7705应用注意要点：
（1） DRDY逻辑不要搞反，高电平时等待转换状态，低电平为可以读取转换数据
（2） 系统校准时输入信号要大于所选量程的4/5，否则校准不到32767。
（3） 校准时要等待一定的时间，读取数据也一样，不能超过转换速率。
（4） 一般的应用只要内部校准，这个很简单，只要初始化就可以。如果测量范围不是芯片的范围，可以通过系统校准来实现，满量程校准电压要大于量程的4/5
#include <util/delay.h>
#include <avr/eeprom.h>
#include "ad7705.h"
#include "main.h"
#include "crc16.h"
#include "Usart.h"
//针对四个量程的设置寄存器的设置内容
//（1）对于单极性V级别输入0-5V、0-20mA、0-10V这三个量程，输入范围为0-2V，无极性，增益为1，缓冲模式--0-2V
//（2）对于双极性V级别输入+-2.5V、+-5V这两个量程，输入范围为+-1V，双极性，增益为2，缓冲模式--+-2V
//（3）对于双精度mV级别输入+-500mV，增益为4，双极性，缓冲模式--+-2V
//（4）对双精度mV级别+-50mV，增益为32，双极性，缓冲模式--+-1.6V
//------MD1(0) MD0(0) G2(0) G1(0) G0(0) B/U(0) BUF(0) FSYNC(0)--------------------------//
const unsigned char text_of_setup[4]={0X04,0X08,0X10,0X28}; //非缓冲模式,数字滤波同步
//const unsigned char text_of_setup[4]={0X06,0X0A,0X12,0X2A}; //缓冲模式，数字滤波同步
extern volatile unsigned char command[7]; //校准命令全局数组
extern volatile unsigned char scale; //记录系统量程
extern volatile unsigned char NO_CALI_TYPE; //未校准类型
extern volatile unsigned long int ZS,GS; //当前量程的校准系数
extern volatile unsigned char time_count; //超时标志
//----------------------------------------------------------------------------
//函数：reset_AD7705
//功能：AD7705串行接口失步后将其复位。复位后要延时500us再访问
//参数：无
//返回：无
//变量：无
//备注：无
//----------------------------------------------------------------------------
void reset_AD7705(void)
{
unsigned char i;
AD_DIN1;
for( i=0; i<36; i++ )
{
AD_CLK0;
asm("nop");
asm("nop");
asm("nop");
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
}
_delay_ms(1);
}
//------------------------------------------------------------------------------------------
//函数：read_AD7705_byte
//功能：从AD7705读一个字节的数据
//参数：无
//返回：读到的一字节数据
//变量：无
//备注：无
//------------------------------------------------------------------------------------------
unsigned char read_AD7705_byte(void)
{
unsigned char data = 0;
unsigned char i = 0;
for( i=0; i<8; i++ )
{
data <<= 1;
AD_CLK0;
asm("nop");
asm("nop");
asm("nop");
if(AD_DOUT)
{
data++;
}
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
}
return data;
}
//------------------------------------------------------------------------------------------
//函数：read_AD7705_word
//功能：从AD7705读一个字的数据，共16bit
//参数：无
//返回：读到的一字节数据
//变量：无
//备注：无
//------------------------------------------------------------------------------------------
unsigned int read_AD7705_word(void)
{
unsigned int data = 0;
unsigned char i = 0;
for( i=0; i<16; i++ )
{
data <<= 1;
AD_CLK0;
asm("nop");
asm("nop");
asm("nop");
if(AD_DOUT)
{
data++;
}
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
}
return data;
}
//------------------------------------------------------------------------------------------
//函数：read_AD7705_dword
//功能：从AD7705读一个24的数据
//参数：无
//返回：读到的一字节数据
//变量：无
//备注：AD7705是一个24位AD，选定刷新频率在16.7HZ下，有效位是19位，暂时读出全部24位数据
//------------------------------------------------------------------------------------------
unsigned long int read_AD7705_dword(void)
{
unsigned long data = 0;
unsigned char i = 0;
for( i=0; i<24; i++ )
{
data <<= 1;
AD_CLK0;
asm("nop");
asm("nop");
asm("nop");
if(AD_DOUT)
{
data++;
}
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
}
return data;
}
//------------------------------------------------------------------------------------------
//函数：write_AD7705_byte
//功能：往AD7705写8位数据
//参数：IN - uint8_t data,要写入AD7705的数据
//返回：无
//变量：无
//备注：无
//------------------------------------------------------------------------------------------
void write_AD7705_byte(unsigned char data)
{
for(unsigned char i=0; i<8; i++)
{
AD_CLK0;
if(data&0x80)
AD_DIN1;
else
AD_DIN0;
asm("nop");
asm("nop");
asm("nop");
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
data <<= 1;
}
AD_DIN1;
}
//------------------------------------------------------------------------------------------
//函数：write_AD7705_dword
//功能：往AD7705写24位数据,因为AD7705是24位的器件
//参数：IN - int32_t data,要写入AD7705的数据
//返回：无
//变量：无
//备注：无
//------------------------------------------------------------------------------------------
void write_AD7705_dword(unsigned long int data)
{
for(unsigned char i = 0; i<24; i++)
{
AD_CLK0;
if(data&0x800000)
AD_DIN1;
else
AD_DIN0;
asm("nop");
asm("nop");
asm("nop");
AD_CLK1;
asm("nop");
asm("nop");
asm("nop");
data <<= 1;
}
AD_DIN1;
}
//--------------------------------------------------------------------------
//-------------------------读取AD7705转换数据函数--------------------------
//入口参数：指向main()主函数定义的ad_data变量的常量指针
//--------------------------------------------------------------------------
void ReadData7705(unsigned int *const pdata)
{
unsigned int data=0, fiter[5]={0};
unsigned long int temp=0;
unsigned char i=0, sort_flag=1;
AD_CS0;
_delay_us(5);
start_AD7705();
for( i=0; i<5; i++ )
{
start_timer0();
_delay_ms(2);
while( AD_DRDY )
{
if( time_count >= time_read_data )
{
stop_timer0();
AD_CS1;
return;
}
}
stop_timer0();
write_AD7705_byte( RD_DATA_REG );
fiter[i] = read_AD7705_word();
}
AD_CS1;
sort_flag = 1;
while( sort_flag )
{
sort_flag = 0;
for( i=0; i<4; i++ )
{
if( fiter[i] > fiter[i+1] )
{
data = fiter[i];
fiter[i] = fiter[i+1];
fiter[i+1] = data;
sort_flag = 1;
}
}
}
temp = ( (unsigned long int)fiter[1] + (unsigned long int)fiter[2]
+ (unsigned long int)fiter[3] )/3;
data = (unsigned int)temp;
if( (data<0xfff0) && (data&0x000f)>0x0008 )
{
data >>= 4;
data++;
}
else
{
data >>= 4;
}
if( 1 != scale )
{
data -= 0x0800;
}
*pdata = data & 0x0fff;
}
//---------------------------------------------------------------------------------------
//校准命令格式
//STX Data Long Command Code Parameter CheckSum ETX
//0x55 数据长度（2） 量程指示 00H/01H CRC16(2) 0x0D
void AD7705_calibration(void)
{
unsigned char readtimes =0;
unsigned char cali_scale =0;
unsigned long int temp =0;
unsigned char coefficient[8] ={0}; //test[8]={0};
//16位校验和的临时变量
unsigned int crcvalue =0;
AD_CS1;
cali_scale = command[2]; //获取上位机发送的要校准的量程类型
eeprom_busy_wait();
eeprom_read_block( &coefficient[0], (void*)(ADDR_EEPROM_1+(cali_scale-1)*10), 8 );
crcvalue = checksum( &coefficient[0], 6 );
if( (coefficient[7]*256+coefficient[6]) != crcvalue )
{
readtimes++;
}
if( 1 == readtimes )
{
eeprom_busy_wait();
eeprom_read_block( &coefficient[0], (void*)(ADDR_EEPROM_2+(cali_scale-1)*10), 8 );
crcvalue = checksum( &coefficient[0], 6 ); //
if( (coefficient[7]*256+coefficient[6]) != crcvalue )
{
readtimes++;
}
}
if( 2 == readtimes )
{
eeprom_busy_wait();
eeprom_read_block( &coefficient[0], (void*)(ADDR_EEPROM_3+(cali_scale-1)*10), 8 );
}
ADDR409_MASK;
AD_CS0;
_delay_us(5);
reset_AD7705();
write_AD7705_byte( WR_CLOCK_REG );
write_AD7705_byte( CLOCK_REG_SET );
if( ZERO_CALIBRATION == command[3] ) //校准命令为零校准
{
write_AD7705_byte( WR_SETUP_REG );
write_AD7705_byte( text_of_setup[cali_scale-1] | SYS_ZERO_CALI);
//等待校准完成
start_timer0();
while( time_count < time_sys_cali );
stop_timer0();
while( AD_DRDY );
//读OFFSET寄存器
write_AD7705_byte( RD_OFFSET_REG );
temp = read_AD7705_dword();
if( cali_scale == scale)
{
ZS = temp; NO_CALI_TYPE = NO_FULL_CALIBRATION;
}
coefficient[0] = (unsigned char)( temp%256 );
coefficient[1] = (unsigned char)( (temp/256)%256 );
coefficient[2] = (unsigned char)( (temp/65536)%256 );
}
else if( FULL_CALIBRATION == command[3] )
{
temp = (unsigned long int)(coefficient[0]) + (unsigned long int)(coefficient[1])*256
+ (unsigned long int)(coefficient[2])*65536;
write_AD7705_byte( WR_OFFSET_REG );
write_AD7705_dword( temp );
write_AD7705_byte( WR_SETUP_REG );
write_AD7705_byte( text_of_setup[cali_scale-1] | SYS_FULL_CALI );
//等待校准完成
start_timer0();
while( time_count < time_sys_cali );
stop_timer0();
while( AD_DRDY );//
//读FULL寄存器
write_AD7705_byte( RD_FULL_REG );
temp = read_AD7705_dword();
if( cali_scale == scale )
{
GS = temp;
NO_CALI_TYPE = ALREADY_CALIBRATION;
}
coefficient[3] = (unsigned char)( temp%256 );
coefficient[4] = (unsigned char)( (temp/256)%256 );
coefficient[5] = (unsigned char)( (temp/65536)%256 );
}
else
{
AD_CS1;
_delay_us(5);
return;
}
AD_CS1;
_delay_us(5);
crcvalue = checksum(&coefficient[0],6);
coefficient[6] = (unsigned char)(crcvalue%256);//
coefficient[7] = (unsigned char)(crcvalue/256);
eeprom_busy_wait();
eeprom_write_block( &coefficient[0], (void*)(ADDR_EEPROM_1+(cali_scale-1)*10), 8 );
eeprom_busy_wait();
eeprom_write_block( &coefficient[0], (void*)(ADDR_EEPROM_2+(cali_scale-1)*10), 8 );
eeprom_busy_wait();
eeprom_write_block( &coefficient[0], (void*)(ADDR_EEPROM_3+(cali_scale-1)*10), 8 );
Txout( &coefficient[0] );//输出校准数据给上位机
return;
}
//
void start_AD7705(void)
{
reset_AD7705();
//写OFFSET寄存器
write_AD7705_byte( WR_OFFSET_REG );
write_AD7705_dword( ZS );
//写满量程校准寄存器
write_AD7705_byte( WR_FULL_REG );
write_AD7705_dword( GS );
//CLOCK寄存器设置，无分频，50HZ输出更新速率
write_AD7705_byte( WR_CLOCK_REG );
write_AD7705_byte( CLOCK_REG_SET );
//写设置寄存器
write_AD7705_byte( WR_SETUP_REG );
write_AD7705_byte( text_of_setup[scale-1] );
start_timer0();
while( time_count < time_read_data );
stop_timer0();
}
(本文引自www.mcujl.com/article.asp?conID=432)
