char s_write_byte(unsigned char value)
{
IIC_DATA_OUT;
unsigned char i,error=0;
for (i=0x80;i>0;i/=2) //shift bit for masking
{
Delay(2);
if (i & value) DQDATA=1; //masking value with i , write to SENSI-BUS
else DQDATA=0;
Delay(2);
SCK=1; //clk for SENSI-BUS
Delay(2); //pulswith approx.5 us
SCK=0;
}
Delay(4);
DQDATA=1; //release DATA-line
IIC_DATA_IN;
SCK=1; //clk #9 for ack
Delay(2);
error=DQDATA; //check ack (DATA will be pulled down by SHT11)
SCK=0;
return error; //error=1 in case of no acknowledge
}
char s_read_byte(unsigned char ack)
{
unsigned char i,val=0;
DQDATA=1; //release DATA-line
IIC_DATA_IN;
for (i=0x80;i>0;i/=2) //shift bit for masking
{
Delay(2);
SCK=1; //clk for SENSI-BUS
Delay(2);
if (DQDATA) val=(val | i); //read bit
SCK=0;
}
Delay(2);
IIC_DATA_OUT;
DQDATA=!ack; //in case of "ack==1" pull down DATA-Line
//----------------------------------------------------------------------------------
char s_softreset(void)
//----------------------------------------------------------------------------------
// resets the sensor by a softreset
{
unsigned char error=0;
s_connectionreset(); //reset communication
error+=s_write_byte(RESET); //send RESET-command to sensor
return error; //error=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_read_statusreg(unsigned char *p_value, unsigned char *p_checksum)
//----------------------------------------------------------------------------------
// reads the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error=s_write_byte(STATUS_REG_R); //send command to sensor
*p_value=s_read_byte(ACK); //read status register (8-bit)
*p_checksum=s_read_byte(noACK); //read checksum (8-bit)
return error; //error=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_write_statusreg(unsigned char *p_value)
//----------------------------------------------------------------------------------
// writes the status register with checksum (8-bit)
{
unsigned char error=0;
s_transstart(); //transmission start
error+=s_write_byte(STATUS_REG_W);//send command to sensor
error+=s_write_byte(*p_value); //send value of status register
return error; //error>=1 in case of no response form the sensor
}
//----------------------------------------------------------------------------------
char s_measure(unsigned char *p_value, unsigned char *p_checksum, unsigned char mode)
//----------------------------------------------------------------------------------
// makes a measurement (humidity/temperature) with checksum
{
unsigned error=0;
unsigned int i;
s_transstart(); //transmission start
switch(mode){ //send command to sensor
case TEMP : error+=s_write_byte(MEASURE_TEMP); break;
case HUMI : error+=s_write_byte(MEASURE_HUMI); break;
default : break;
}
DQDATA=1; //release DATA-line
IIC_DATA_IN;
for (i=0;i<65535;i++)
{
Delay(10);
if(DQDATA==0) break;//wait until sensor has finished the measurement
}
//for (i=0;DQDATA && i<75000;i++) //test--i=21995 or 6327
// { } //wait until sensor has finished the measurement
if(DQDATA) error+=1; // or timeout (~2 sec.) is reached
*(p_value) =s_read_byte(ACK); //read the first byte (MSB)
*(p_value+1)=s_read_byte(ACK); //read the second byte (LSB)
*p_checksum =s_read_byte(noACK); //read checksum
return error;
}
//----------------------------------------------------------------------------------------
void calc_sth10(float *p_humidity ,float *p_temperature)
//----------------------------------------------------------------------------------------
// calculates temperature [癈] and humidity [%RH]
// input : humi [Ticks] (12 bit)
// temp [Ticks] (14 bit)
// output: humi [%RH]
// temp [癈]
{
const float C1=-4.0; // for 12 Bit
const float C2=+0.0405; // for 12 Bit
const float C3=-0.0000028; // for 12 Bit
const float T1=+0.01; // for 14 Bit @ 5V
const float T2=+0.00008; // for 14 Bit @ 5V
float rh=*p_humidity; // rh: Humidity [Ticks] 12 Bit
float t=*p_temperature; // t: Temperature [Ticks] 14 Bit
float rh_lin; // rh_lin: Humidity linear
float rh_true; // rh_true: Temperature compensated humidity
float t_C; // t_C : Temperature [癈]
t_C=t*0.01 - 40; //calc. temperature from ticks to [癈]
rh_lin=C3*rh*rh + C2*rh + C1; //calc. humidity from ticks to [%RH]
rh_true=(t_C-25)*(T1+T2*rh)+rh_lin; //calc. temperature compensated humidity [%RH]
if(rh_true>100)rh_true=100; //cut if the value is outside of
if(rh_true<0.1)rh_true=0.1; //the physical possible range
*p_temperature=t_C; //return temperature [癈]
*p_humidity=rh_true; //return humidity[%RH]
}
//主测量里调用
Derror+=s_measure((unsigned char*) &humi_val.i,&checksum,HUMI); //measure humidity
Derror+=s_measure((unsigned char*) &temp_val.i,&checksum,TEMP); //measure temperature
if(Derror!=0) s_connectionreset(); //in case of an error: connection reset
else
{
humi_val.f=(float)humi_val.i; //converts integer to float
temp_val.f=(float)temp_val.i; //converts integer to float
calc_sth10(&humi_val.f,&temp_val.f); //calculate humidity, temperature