调了两天，MSP430始终接收不到数据，一直以为是代码的问题，今天无意中看到别人的一片文章，才发现问题出在上拉电阻上。DATA线的上拉电阻不能太大，10k不行，换成了1k就没问题了。mark一下，顺便感谢那位作者，附上他的链接：http://blog.sina.com.cn/s/blog_52f5ded30100bf68.html
附上MSP430代码：
在main里调用：
s_connectionreset();
s_write_status();
for(;;)
{
s_read_temp_and_humi();//读取温度、湿度
}
sht11.h：
enum {TEMP,HUMI};
#define S_DATA_OUT (P6DIR |= BIT3) //P6.5 OUT
#define S_DATA_IN (P6DIR &=~BIT3) //P6.5 IN
#define S_DATA (P6IN & BIT3) //P6.5 DATA
#define S_DATA_LOW (P6OUT &=~BIT3)
#define S_DATA_HIGH (P6OUT |= BIT3)
#define S_SCK_OUT (P6DIR |= BIT4)
#define S_SCK_LOW (P6OUT &=~BIT4)
#define S_SCK_HIGH (P6OUT |= BIT4)
#define noACK 0
#define ACK 1
//adr command r/w
#define MEASURE_TEMP 0x03 //000 0001 1
#define MEASURE_HUMI 0x05 //000 0010 1
#define MEASURE_STATUS 0x06 //000 0011 0
void delay(unsigned int k);
void s_transstart(void);
void s_connectionreset(void);
unsigned char s_write_byte(unsigned char value);
unsigned char s_read_byte(unsigned char ack);
void s_calc_sth11(void);
unsigned char s_measure(unsigned int *p_value, unsigned char mode);
void s_write_status();
void s_read_temp_and_humi(void);
unsigned int temperature,humidity;
float f_temperature,f_humidity;
unsigned char s_read_data(unsigned int *p_value);
unsigned char s_measure_cmd(unsigned char mode);
unsigned char s_error=0;
extern float humi;
/******************************************************************************/
/* Temperature and humidity sensor function start */
/******************************************************************************/
// generates a tran××ission start
// _____ ________
// DATA: |_______|
// ___ ___
// SCK : ___| |___| |______
// calculates temperature [懊] and humidity [%RH]
// input : humi [Ticks] (12 bit)
// temp [Ticks] (14 bit)
// output: humi [%RH]
// temp [懊]
void s_calc_sth11(void)
{
float rh; // rh: Humidity
float t; // t: Temperature
float ttt;
if(temperature>7000)
ttt=temperature-7000;
else
ttt=7000-temperature;
t=temperature*0.01 - 39.64-0.00000002*ttt*ttt; //calc. temperature from ticks to [℃]
rh=(0.0405-0.0000028*humidity)*humidity -4.0; //calc. humidity from ticks to [%RH]
rh=(t-25)*(0.01+0.00008*humidity)+rh; //calc. temperature compensated humidity [%RH]
f_temperature=t;
temperature=t; //return temperature [℃]
f_humidity=rh;
humidity=rh; //return humidity[%RH]
if((t-temperature)>=0.5)
temperature+=1;
if((rh-humidity)>=0.5)
humidity+=1;
if(humidity>100) humidity=100; //cut if the value is outside of
if(humidity<1) humidity=1; //the physical possi××e range
humi=0.123;
}
void s_transstart(void)
{
S_DATA_OUT;
S_SCK_OUT;
S_DATA_HIGH; //Initial state
S_SCK_LOW;
S_SCK_HIGH;
S_DATA_LOW;
S_SCK_LOW;
S_SCK_HIGH;
S_DATA_HIGH;
S_SCK_LOW;
}
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart
// _____________________________________________________ ________
// DATA: |_______|
// _ _ _ _ _ _ _ _ _ ___ ___
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______| |___| |______
void s_connectionreset(void)
{
unsigned char i;
S_DATA_OUT;
S_SCK_OUT;
S_DATA_HIGH; //Initial state
S_SCK_LOW;
for(i=0;i<9;i++) //9 SCK cycles
{
S_SCK_HIGH;
//_nop();
S_SCK_LOW;
}
s_transstart(); //tran××ission start
}
// writes a byte on the Sensibus and checks the acknowledge
unsigned char s_write_byte(unsigned char value)
{
unsigned char i,error=0;
S_DATA_OUT;
for (i=0x80;i>0;i/=2) //shift bit for masking
{
if (i & value) S_DATA_HIGH; //masking value with i , write to SENSI-BUS
else S_DATA_LOW;
S_SCK_HIGH; //clk for SENSI-BUS
S_SCK_LOW;
}
S_DATA_IN;
S_SCK_HIGH; //clk #9 for ack
error=S_DATA; //check ack (DATA will be pulled down by SHT11)
S_SCK_LOW;
S_DATA_OUT; //release DATA-line
return error; //error=1 in case of no acknowledge
}
// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"
unsigned char s_read_byte(unsigned char ack)
{
unsigned char i,val=0;
S_DATA_IN;
for (i=0x80;i>0;i/=2) //shift bit for masking
{
S_SCK_HIGH; //clk for SENSI-BUS
if (S_DATA) val=(val | i); //read bit
S_SCK_LOW;
}
S_DATA_OUT;
if(ack)
S_DATA_LOW;
else
S_DATA_HIGH; //in case of "ack==1" pull down DATA-Line
S_SCK_HIGH; //clk #9 for ack
S_SCK_LOW; //release DATA-line
return val;
}
/*Write status register:12bit humi,14bit temp*/
void s_write_status(void)
{
s_connectionreset();
s_write_byte(MEASURE_STATUS);
s_write_byte(0x00);
}
// makes a measurement (humidity/temperature)
unsigned char s_measure(unsigned int *p_value,unsigned char mode)
{
unsigned char error=0;
unsigned int i;
s_transstart(); //tran××ission start
if(mode==TEMP) //send command to sensor
error+=s_write_byte(MEASURE_TEMP);
else
error+=s_write_byte(MEASURE_HUMI);
S_DATA_IN;
for (i=0;i<65535;i++)
if(S_DATA==0) break; //wait until sensor has finished the measurement
if(S_DATA) error+=1; // or timeout (~1 sec.) is reached
*p_value =s_read_byte(ACK); //read the first byte (MSB)
*p_value = (*p_value)<<8;
(*p_value) +=s_read_byte(noACK); //read the second byte (LSB)
return error;
}
/***mode:TEMP,HUMI***/
unsigned char s_measure_cmd(unsigned char mode)
{
unsigned char error=0;
s_transstart();
if(mode==TEMP) //send command to sensor
error+=s_write_byte(MEASURE_TEMP);
else
error+=s_write_byte(MEASURE_HUMI);
S_DATA_IN;
return error;
}
unsigned char s_read_data(unsigned int *p_value)
{
if(S_DATA)
return 1;
else
{
*p_value =s_read_byte(ACK); //read the first byte (MSB)
*p_value = (*p_value)<<8;
(*p_value) +=s_read_byte(noACK); //read the second byte (LSB)
return 0;
}
}
// measure humidity [%RH](8 bit) and temperature [℃](12 bit)
void s_read_temp_and_humi(void)
{
unsigned char error=1;
while(error)
{
error=0;
error+=s_measure(&humidity,HUMI); //measure humidity
error+=s_measure(&temperature,TEMP); //measure temperature
if(error!=0)
s_connectionreset(); //in case of an error: connection reset
else
s_calc_sth11(); //calculate humidity, temperature
}
}
/******************************************************************************/
/* Temperature and humidity sensor function END */
/******************************************************************************/
void delay(unsigned int k)
{
unsigned int ktemp;
for(ktemp=0;ktemp<k;ktemp++);
}