屬于msp430的串行接口傳輸數據的應用。SHTxx的串行接口與IIC不兼容，但其軟件實現與IIC類似。

使用器件型號：msp430F169/msp430F149，SHT70@SENSIRION AG

典型應用電路：

代碼：

#include

#include "intrinsics.h"

#include      

typedef unsigned int  uint;

typedef unsigned char uchar;

char write_byte(uchar value);

char read_byte(uchar ack);

void transstart(void);

void connectionreset(void);

char softreset(void);

char read_statusreg(uchar *p_value, uchar *p_checksum);

char write_statusreg(uchar *p_value);

char measure(unsigned short int*p_value, uchar *p_checksum, uchar mode);

void calc_sth(unsigned short int t, unsigned short int rh, float *p_temperature, float *p_humidity);

float calc_dewpoint(float h,float t);

void sht10_init(void);

void CLK_Init();

   float humi_val_real=0.0;   

   float temp_val_real=0.0;

   float dew_point=0.0;

#define noACK 0

#define ACK   1

#define DATA_OUT  P5DIR |= BIT3

#define DATA_IN   P5DIR &=~BIT3

#define DATA_RIN  (P5IN & BIT3)

#define DATA_H P5OUT |= BIT3 //DATA <---> P5.1

#define DATA_L P5OUT &=~ BIT3 

#define SCK_H  P5OUT |= BIT4  //SCK  <---> P5.2

#define SCK_L  P5OUT &=~ BIT4

#define REG_W 0x06  // 0000 0110

#define REG_R 0x07  // 0000 0111

#define TEMP  0x03  // 0000 0011

#define HUMI  0x05  // 0000 0101

#define RESET 0x1e  // 0001 1111

#define CPU_F ((double)8000000) 

#define delay_us(x) __delay_cycles((long)(CPU_F*(double)x/1000000.0))

#define delay_ms(x) __delay_cycles((long)(CPU_F*(double)x/1000.0))

void delay();

char write_byte(uchar value)

//write a byte on the sensibus and checks the ackonwledge

{

  uchar i,error = 0;

  DATA_OUT;

  for(i=0x80;i>0;i/=2)

  {

    if(i&value)

    {DATA_OUT;DATA_H;}

    else

    {DATA_OUT; DATA_L;}

delay();

    SCK_H;

delay();//5ms

    SCK_L;

delay();

  }

   DATA_IN; 

  SCK_H;

     //delay_ms(800);

  error = DATA_RIN;

  SCK_L;

  return error;

}

char read_byte(uchar ack)

// read a byte from sensibus and gives an ackowledge in case of 'ack =1'

{

  uchar i,val=0;

  DATA_IN;

  for (i=0x80;i>0;i/=2)             //shift bit for masking

  { 

delay();

    SCK_H;                          //clk for SENSI-BUS

delay();

    if (DATA_RIN) 

      val=(val | i);        //read bit  

    SCK_L;   

  }

  DATA_OUT;

  if(ack) 

    DATA_L;

  else

    DATA_H;

  delay();

  SCK_H;                            //clk #9 for ack

  delay();          //pulswith approx. 5 us 

  SCK_L;     

  delay();                        

  return val;

}

void transstart(void)

{

  DATA_OUT;

  DATA_H;SCK_L;

delay();

  SCK_H;

delay();

  DATA_L;

delay();

  SCK_L;

delay();

  SCK_H;

delay();

  DATA_H;

delay();

  SCK_L;

}

void connectionreset(void)

{

  uchar i;

  DATA_OUT;

  DATA_H;

  SCK_L;

  for(i=0;i<9;i++)

  {

    SCK_H;

  delay();

    SCK_L;

  delay();

  }

  transstart();

}

char softreset(void)

{

  uchar error = 0;

  connectionreset();

  error += write_byte(RESET);

  return error;

}

char read_statusreg(uchar *p_value, uchar *p_checksum)

//----------------------------------------------------------------------------------

// reads the status register with checksum (8-bit)

{ 

  uchar error=0;

  transstart();                   //transmission start

  error=write_byte(REG_R); //send command to sensor

  *p_value=read_byte(ACK);        //read status register (8-bit)

  *p_checksum=read_byte(noACK);   //read checksum (8-bit)  

  return error;                     //error=1 in case of no response form the sensor

}

//----------------------------------------------------------------------------------

char write_statusreg(uchar *p_value)

//----------------------------------------------------------------------------------

// writes the status register with checksum (8-bit)

{ 

  uchar error=0;

  transstart();                   //transmission start

  error+=write_byte(REG_W);//send command to sensor

  error+=write_byte(*p_value);    //send value of status register

  return error;                     //error>=1 in case of no response form the sensor

}

//----------------------------------------------------------------------------------

char measure(unsigned short int*p_value, uchar *p_checksum, uchar mode)

//----------------------------------------------------------------------------------

// makes a measurement (humidity/temperature) with checksum

{ 

  uchar error=0;

  unsigned short int i;

  uchar value_H = 0,value_L = 0;

  transstart();                   //transmission start

  switch(mode){                     //send command to sensor

  case TEMP:

      error+=write_byte(TEMP); 

      break;

  case HUMI:

      error+=write_byte(HUMI);

      break;

  default:

      break;  

  }

  DATA_IN;

  for (i=0;i<250;i++)

  {  

delay();

delay();

delay();

delay();

    if(DATA_RIN == 0) 

      break;

  } //wait until sensor has finished the measurement

  if(DATA_RIN == 1) error+=1;                // or timeout (~2 sec.) is reached

  value_H=read_byte(ACK);    //read the first byte (MSB)

  value_L =read_byte(ACK);    //read the second byte (LSB)

  *p_checksum =read_byte(noACK);  //read checksum

  *p_value = (value_H << 8) | value_L;

  return error;

}

void calc_sth(unsigned short int t, unsigned short int rh, float *p_temperature, float *p_humidity)

{

const float d1 = -39.61;         //@3.3V

const float d2 = +0.01;          //for 14 bit

//for 12 bit

const float C1 = -2.0468;        

const float C2 = +0.0367;

const float C3 = -0.0000015955;

//for 12 bit

const float T1 = +0.01;

const float T2 = +0.00008;

float RH_Lin; 

float RH_Ture;

float temp_C;

temp_C = d1 + d2 * t;                             

RH_Lin = C1 + C2 * rh + C3 * rh * rh;            

RH_Ture = (temp_C -25) * (T1 + T2 * rh) + RH_Lin; 

if(RH_Ture > 100)  

RH_Ture = 100;

if(RH_Ture < 0.1f)

RH_Ture = 0.1;  

*p_humidity = RH_Ture;

*p_temperature = temp_C;

}

float calc_dewpoint(float t,float h)

{ 

float dew_point;

float m=17.62,Tn=243.12; //default

if(-40<=t && t<0)

{

m  = 22.46;

Tn = 272.62;

}

dew_point = Tn*(log10(h)+m*t/(Tn+t))/(m-log10(h)-+m*t/(Tn+t));

return dew_point;

}

void sht10_init(void)

{

  P5SEL = 0x00;

 // P5SEL |=BIT2;

 // P5SEL &=~ BIT1;

 // P5DIR &=~BIT1;

  //P5DIR |= BIT2;

  //DATA_OUT;

  P5DIR |= BIT3+BIT4;

}

void CLK_Init()

{

unsigned int iq0;

   //BCSCTL1&=~0X00;                      //打開XT2振蕩器

   BCSCTL1 &= ~XT2OFF;         //打開XT振蕩器

   do

   {

      IFG1 &= ~OFIFG;                   // 清除振蕩器失效標志

      for (iq0 = 0xFF; iq0 > 0; iq0--); // 延時，等待XT2起振

    }

    while ((IFG1 & OFIFG) != 0);        // 判斷XT2是否起振

    //BCSCTL2 =SELM_2+SELS;               //選擇MCLK、SMCLK為XT2

    BCSCTL2 |= SELM1+SELS;      //MCLK為8MHZ，SMCLK為8MHZ

}

int main(void)

{ 

  unsigned short int humi_val=0,temp_val=0;

  uchar error=0,checksum=0;

  WDTCTL=WDTPW+WDTHOLD;

  //int i;

   CLK_Init();

  sht10_init();

  connectionreset();

  while(1)

  { 

    error=0;

    error+=measure(&temp_val,&checksum,TEMP);  //measure temperature

    error+=measure(&humi_val,&checksum,HUMI);  //measure humidity

    if(error!=0) 

      connectionreset();                 

    else

    {                   

       calc_sth(temp_val,humi_val,&temp_val_real, &humi_val_real);            //calculate humidity, temperature

       dew_point = calc_dewpoint(temp_val_real, humi_val_real); 

      //printf("%2.1f℃  %2.1f%% %2.1f℃rn", temp_val_real, humi_val_real, dew_point);

    }

    //----------wait approx. 0.8s to avoid heating up SHTxx------------------------------      

    delay();

    delay();

    delay();