ADS1115与MSP430的使用

ADS1115是超小型的，宽电压16位AD转换器，通过一个I2c接口与MCU相连，官方给的电路连接图如下

驱动程序如下

#include<msp430g2553.h>
#include "ads1115.h"

void delay()
{
  uint i;
  for(i=0;i<20000;i++);
}

void wait()
{
  uchar i=3;
  while(i--);
  _NOP();
}
void start()
{
  S_SDA;                  //数据线拉高
  wait();
  S_SCL;                  //时钟为高
  wait();
  C_SDA;                  //数据线拉低，表起始信号
  wait();
  C_SCL;                  //时钟为低，允许数据改变
  wait();
}
void stop()
{
  C_SCL;
  wait();
  C_SDA;
  wait();
  S_SCL;
  wait();
  S_SDA;                  //在SCL为高器期间，数据线上升，表停止
}

void ack()            //应答
{
  C_SDA;
  wait();
  S_SCL;
  wait();
  C_SCL;
  wait();
  S_SDA;
}

uchar check_ack()
{
  uchar ack;
  S_SDA;
  wait();
  S_SCL;
  wait();
  ack=SDA & 0x80;
  C_SCL;
  _NOP();
  if(ack) return 1;          //无应答
  else    return 0;          //有应答
}

void write_byte(uchar byte)
{
  uchar i;
  C_SCL;
  for(i=0;i<8;i++)
  {
    if(byte & 0x80) S_SDA;
    else            C_SDA;   //送数据
    wait();
    S_SCL;                   //拉高控制线
    wait();
    C_SCL;                  //拉低时钟线，允许数据改变
    byte <<= 1;             //准备下一位
  }
}

uchar read_byte(void)
{
  uchar byte=0,i;
  P1DIR &= ~BIT7;
  wait();
  for(i=0;i<8;i++)
  {
    S_SCL;
    wait();
    byte <<= 1;
    if(SDA & 0X80) byte |= 0x01;
    C_SCL;
    wait();
  }
  return byte;
}

void write_word(uchar addr,uint word)
{
  uchar byte=0x90;           //0b10010000
  start();
  write_byte(byte);          //写地址
  byte = check_ack();
  write_byte(addr);          //指定寄存器
  byte = check_ack();
  write_byte(word>>8);     //写高字节
  byte = check_ack();
  write_byte(word);        //写低字节
  byte = check_ack();
  stop();
}

uint read_word(uchar addr)
{
  uint  word;
  uchar byte=0x90;            //0b10010000
  start();
  write_byte(byte);           //写地址
  byte = check_ack();
  write_byte(addr);           //指定寄存器
  byte = check_ack();
  stop();
  wait();
  start();
  byte=0x91;                  //0b10010001
  write_byte(byte);           //写地址,操作为读
  byte = check_ack();
  word = read_byte();         //读高字节
  ack();
  word <<= 8;
  byte = read_byte();         //读低字节
  ack();
  word += byte;  
  stop();
  return word;
}

void main(void)
{
  uint value;
  uint tmp;
  float u;
  WDTCTL=WDTPW+WDTHOLD;
  P1DIR |= BIT1;
  P1OUT &= ~BIT7;
  stop();
  while(1)
  {
    write_word(0x01,0xc383);        //0b1100 0011 1000 0011
    delay();
    value = read_word(0x00);        //读取值
    tmp = value & 0x7fff;
    u = 4.096 * tmp / 32768;
    if(value>0x7fff) u = 0.0;
    u *= 1000;
  }
}

ADS1115的时序要求比较严格，针对不同的MCU移植时需要注意时间