ADS1255使用中误差的解决

ADS1255与MCU的连接就不用说了，很简单的，采用IO模拟时序

C8051的芯片与ADS1255相连，刚开始的时候采集到的数据与输入的信号有误差，大概有%1左右，然后输入短接到地，大概有2mv的电压，检查了好久，最后才发现将STATUS寄存器的BUFEN置1后，输入短接到地，有10uv左右电压，注意，将BUFEN置1后可以提高输入阻抗，减小误差

程序如下：

#include <avr/io.h>
#include <avr/iom32.h>
#include <string.h>
#include <avr/interrupt.h>
#include <compat/deprecated.h>

//PORT B
#define ADS1255_SYNC	PORT3
#define ADS1255_DRDY	PORT2
#define ADS1255_CS		PORT4

#define SPI_SS			ADS1255_CS
#define SPI_MOSI		PORT5
#define SPI_MISO		PORT6
#define SPI_SCLK		PORT7

#define SW_EN			PB0
#define Alarm			PD4


void init_spi(void);
uint8_t DoByte(uint8_t byte);
void do_n_byte(uint8_t length,uint8_t* pSend);
uint32_t read_data(void);
uint8_t read_register(uint8_t addr);
void write_register(uint8_t addr,uint8_t data);
void set_standby(void);
void set_wakeup(void);
void set_sync(void);
void set_selfcal(void);
uint32_t read_standby(void);

uint32_t tmp=0;
	uint8_t i = 0;
	uint32_t sum=0,temp=0;max=0,min=0xffffff,p2p=0;
	uint32_t result[50];

ISR(INT2_vect) 
{
	tmp=read_data();
if(tmp&0x00800000)
		{tmp &= 0x007fffff;
		}
		else
		{tmp &= 0x007fffff;tmp += 0x7fffff;
		}

		if(i<50) 	i++;else i=0;
	
		result[i] = 0;
		result[i] = tmp;	 
		sum += result[i];

		switch(i)
		{case 50:sum = sum/51;temp=sum; break;default:break;
		}		

}
int main()
{
	cli();
	init_spi();
	DDRB |= (1<<ADS1255_SYNC);   / T OUTPUT
	DDRB &= ~(1<<ADS1255_DRDY);
	PORTB |= (1<<ADS1255_SYNC);


	DDRB |= (1<<SW_EN);
	PORTB |= (1<<SW_EN);//SW_EN disconnect 10*

	DDRD |=(1<<Alarm);

	write_register(0,0xf6);
	write_register(1,0x01);	/ t input pin
	write_register(2,0x20); / t clk pin, pga gain
	write_register(3,0xa1); //1ksps
	write_register(4,0x00); / t gpio


	tmp = read_register(0);
	tmp = read_register(1);
	tmp = read_register(2);
	tmp = read_register(3);
tmp = read_register(4);

	//INT2	initial
	cbi(MCUCSR,ISC2);//falling edge
	sbi(GICR,INT2);//enable INT2
	cbi(GIFR,INTF2);//clear INTF2
/*
	PORTB &= ~(1<<ADS1255_SYNC);
	PORTB |= (1<<ADS1255_SYNC);
*/
	set_sync();
	set_wakeup();
	PORTD |=(1<<Alarm);

	sei();
//loop:

	i = 0;
	tmp = 0;
	max = 0;
	min = 0xffffff;	
while(1);
	{
		if(tmp&0x00800000)
		{tmp &= 0x007fffff;
		}
		else
		{tmp &= 0x007fffff;tmp += 0x7fffff;
		}
		
		result[i] = 0;
		result[i] = tmp;
		if(tmp>max)	max = tmp;
		if(tmp<min) min = tmp;
	}
	
//	p2p = max-min;
//	goto loop;

}
uint32_t read_data(void)
{
	uint8_t send[]={0x01,0xff,0xff,0xff};
	uint32_t data;
	
	do_n_byte(sizeof(send),send);
//	strncpy((uint8_t*)&data,send+1,3);
	data = send[1]*65536 + send[2]*256 +send[1];
	
	return data;
}
/*
uint32_t read_data_c(uint8_t num)
{
	uint8_t send[]={0x03,0xff,0xff,0xff};
	uint32_t data[];
	uint8_t j=0;

	do_n_byte(sizeof(send),send);
	data[0] = send[1]*65536 + send[2]*256 +send[1];
	
	for(;j<num;j++)
	{
		uint8_t send[]={0xff,0xff,0xff};
                  do_n_byte(sizeof(send),send);
		data[j+1] = send[1]*65536 + send[2]*256 +send[1];
	}
	return data;		
}
*/
uint32_t read_standby(void)
{
	uint8_t send[]={0x01,0xff,0xff,0xff,0xfd};
	uint32_t data;	
	
	do_n_byte(sizeof(send),send);
	
	strncpy((uint8_t*)&data,send+1,3);

	return data;
}
void set_selfcal(void)
{
	PORTB &= ~(1<<ADS1255_CS);
	
	DoByte(0xf0);/ lfcal command byte(in order to get the best performance)

	PORTB |= (1<<ADS1255_CS);
}
void set_wakeup(void)
{
	PORTB &= ~(1<<ADS1255_CS);
	
	DoByte(0x00);//wakeup command byte(0xff can too)

	PORTB |= (1<<ADS1255_CS);
}
void set_standby(void)
{

	PORTB &= ~(1<<ADS1255_CS);
	
	DoByte(0xfd);//standby command byte
	
	PORTB |= (1<<ADS1255_CS);
}

void set_sync(void)
{

	PORTB &= ~(1<<ADS1255_CS);
	
	DoByte(0xfc);//sync command byte
	
	PORTB |= (1<<ADS1255_CS);
}
void write_register(uint8_t addr,uint8_t data)
{
	uint8_t send[] = {0x50,0x00,0x00};//write 1 register(as used 0x00)
	send[0] |= addr;//starting from register addr(as used 0101 "addr"b)
	send[2] |= data;//data writed

	do_n_byte(sizeof(send),send);

}

uint8_t read_register(uint8_t addr)
{
	uint8_t send[] = {0x10,0x00,0xff};//read 1 register(as used 0x00)
	send[0] |= addr;//starting from register addr(as used 0001 "addr"b)	

	do_n_byte(sizeof(send),send);

	return send[2];//content saved in the send[2]
}
void init_spi(void)
{
	DDRB = (1<<SPI_MOSI) | (1<<SPI_SCLK) | (1<<SPI_SS);
	DDRB &= ~(0<<SPI_MISO);
	DDRB |= (1<<ADS1255_CS);
    SPCR = (1<<MSTR) | (1<<SPE) | (1<<SPR0) | (0<<CPOL) | (1<<CPHA);
	PORTB |= (1<<ADS1255_CS);
}

uint8_t DoByte(uint8_t byte)
{
    SPDR = byte;
    while (!(SPSR & 0x80));
	return SPDR;
}
void do_n_byte(uint8_t length,uint8_t* pSend)
{

	PORTB &= ~(1<<ADS1255_CS);

	while(length--)
	{
		*pSend = DoByte(*pSend);
		pSend++;
	}

	PORTB |= (1<<ADS1255_CS);
}

应该应用的技术细节, 使用 ADS1255 的朋友也注意一下, 记录一下.

可以中值滤波