在msp430上使用SHT70

属于msp430的串行接口传输数据的应用。SHTxx的串行接口与IIC不兼容，但其软件实现与IIC类似。

使用器件型号：msp430F169/msp430F149，SHT70@SENSIRION AG
典型应用电路：

代码：

#include <msp430x16x.h>
#include "intrinsics.h"
#include <math.h>     

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;                      //打开XT2振荡器
   BCSCTL1 &= ~XT2OFF;         //打开XT振荡器
   do
   {
      IFG1 &= ~OFIFG;                   // 清除振荡器失效标志
      for (iq0 = 0xFF; iq0 > 0; iq0--); // 延时，等待XT2起振
    }
    while ((IFG1 & OFIFG) != 0);        // 判断XT2是否起振
    //BCSCTL2 =SELM_2+SELS;               //选择MCLK、SMCLK为XT2
    BCSCTL2 |= SELM1+SELS;      //MCLK为8MHZ，SMCLK为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℃\r\n", temp_val_real, humi_val_real, dew_point);
    }
    //----------wait approx. 0.8s to avoid heating up SHTxx------------------------------      
    delay();
    delay();
    delay();
  }
}

 void delay()
 {
  for(int i=0;i<300;i++)
    for(int j=0;j<2;j++);
 }