/*********************************************************************************** 
Project:          SHTxx demo program (V2.1) 
Filename:         SHTxx_Sample_Code.c     

Prozessor:        80C51 family 
Compiler:         Keil Version 6.14 

Autor:            MST 
Copyrigth:        (c) Sensirion AG       
***********************************************************************************/ 

#include <AT89s53.h> //Microcontroller specific library, e.g. port definitions 
#include <intrins.h> //Keil library (is used for _nop()_ operation)   
#include <math.h>    //Keil library   
#include <stdio.h>   //Keil library 

typedef union  
{ unsigned int i; 
  float f; 
} value; 

//---------------------------------------------------------------------------------- 
// modul-var 
//---------------------------------------------------------------------------------- 
enum {TEMP,HUMI}; 

#define        DATA           P1_1 
#define        SCK           P1_0 

#define noACK 0 
#define ACK   1 
                            //adr  command  r/w 
#define STATUS_REG_W 0x06   //000   0011    0 
#define STATUS_REG_R 0x07   //000   0011    1 
#define MEASURE_TEMP 0x03   //000   0001    1 
#define MEASURE_HUMI 0x05   //000   0010    1 
#define RESET        0x1e   //000   1111    0 

//---------------------------------------------------------------------------------- 
char s_write_byte(unsigned char value) 
//---------------------------------------------------------------------------------- 
// writes a byte on the Sensibus and checks the acknowledge  
{  
  unsigned char i,error=0;   
  for (i=0x80;i>0;i/=2)             //shift bit for masking 
  { if (i & value) DATA=1;          //masking value with i , write to SENSI-BUS 
    else DATA=0;                         
    SCK=1;                          //clk for SENSI-BUS 
    _nop_();_nop_();_nop_();        //pulswith approx. 5 us           
    SCK=0; 
  } 
  DATA=1;                           //release DATA-line 
  SCK=1;                            //clk #9 for ack  
  error=DATA;                       //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) 
//---------------------------------------------------------------------------------- 
// reads a byte form the Sensibus and gives an acknowledge in case of "ack=1"  
{  
  unsigned char i,val=0; 
  DATA=1;                           //release DATA-line 
  for (i=0x80;i>0;i/=2)             //shift bit for masking 
  { SCK=1;                          //clk for SENSI-BUS 
    if (DATA) val=(val | i);        //read bit   
    SCK=0;                                            
  } 
  DATA=!ack;                        //in case of "ack==1" pull down DATA-Line 
  SCK=1;                            //clk #9 for ack 
  _nop_();_nop_();_nop_();          //pulswith approx. 5 us  
  SCK=0;                                                     
  DATA=1;                           //release DATA-line 
  return val; 
} 

//---------------------------------------------------------------------------------- 
void s_transstart(void) 
//---------------------------------------------------------------------------------- 
// generates a transmission start  
//       _____         ________ 
// DATA:      |_______| 
//           ___     ___ 
// SCK : ___|   |___|   |______ 
{   
   DATA=1; SCK=0;                   //Initial state 
   _nop_(); 
   SCK=1; 
   _nop_(); 
   DATA=0; 
   _nop_(); 
   SCK=0;   
   _nop_();_nop_();_nop_(); 
   SCK=1; 
   _nop_(); 
   DATA=1;                    
   _nop_(); 
   SCK=0;                    
} 

//---------------------------------------------------------------------------------- 
void s_connectionreset(void) 
//---------------------------------------------------------------------------------- 
// communication reset: DATA-line=1 and at least 9 SCK cycles followed by transstart 
//       _____________________________________________________         ________ 
// DATA:                                                      |_______| 
//          _    _    _    _    _    _    _    _    _        ___     ___ 
// SCK : __| |__| |__| |__| |__| |__| |__| |__| |__| |______|   |___|   |______ 
{   
  unsigned char i;  
  DATA=1; SCK=0;                    //Initial state 
  for(i=0;i<9;i++)                  //9 SCK cycles 
  { SCK=1; 
    SCK=0; 
  } 
  s_transstart();                   //transmission start 
} 

//---------------------------------------------------------------------------------- 
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;          
  } 
  for (i=0;i<65535;i++) if(DATA==0) break; //wait until sensor has finished the measurement 
  if(DATA) 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 init_uart() 
//---------------------------------------------------------------------------------- 
//9600 bps @ 11.059 MHz  
{SCON  = 0x52;     
 TMOD  = 0x20;     
 TCON  = 0x69;           
 TH1   = 0xfd;     
} 

//---------------------------------------------------------------------------------------- 
void calc_sth11(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] 
} 

//-------------------------------------------------------------------- 
float calc_dewpoint(float h,float t) 
//-------------------------------------------------------------------- 
// calculates dew point 
// input:   humidity [%RH], temperature [癈] 
// output:  dew point [癈] 
{ float logEx,dew_point; 
  logEx=0.66077+7.5*t/(237.3+t)+(log10(h)-2); 
  dew_point = (logEx - 0.66077)*237.3/(0.66077+7.5-logEx); 
  return dew_point; 
} 

//---------------------------------------------------------------------------------- 
void main() 
//---------------------------------------------------------------------------------- 
// sample program that shows how to use SHT11 functions 
// 1. connection reset  
// 2. measure humidity [ticks](12 bit) and temperature [ticks](14 bit) 
// 3. calculate humidity [%RH] and temperature [癈] 
// 4. calculate dew point [癈] 
// 5. print temperature, humidity, dew point   

{  
  value humi_val,temp_val; 
  float dew_point; 
  unsigned char error,checksum; 
  unsigned int i; 

  init_uart(); 
  s_connectionreset(); 
  while(1) 
  { 
    error=0; 
    error+=s_measure((unsigned char*) &humi_val.i,&checksum,HUMI);  //measure humidity 
    error+=s_measure((unsigned char*) &temp_val.i,&checksum,TEMP);  //measure temperature 
    if(error!=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_sth11(&humi_val.f,&temp_val.f);            //calculate humidity, temperature 
      dew_point=calc_dewpoint(humi_val.f,temp_val.f); //calculate dew point 
      printf("temp:%5.1fC humi:%5.1f%% dew point:%5.1fC 
",temp_val.f,humi_val.f,dew_point); 
    } 
    //----------wait approx. 0.8s to avoid heating up SHTxx------------------------------       
    for (i=0;i<40000;i++);     //(be sure that the compiler doesn't eliminate this line!) 
    //-----------------------------------------------------------------------------------                        
  } 
}