I2C.h

#ifndef I2C_H #define I2C_H  //---------- Includes ---------------------------------------------------------- #include "system.h"  //---------- Defines ----------------------------------------------------------- //I2C ports //The communication on SDA and SCL is done by switching pad direction //For a low level on SCL or SDA, direction is set to output. For a high level on //SCL or SDA, direction is set to input. (pull up resistor active) #define SDA PM3H_bit.no0 //SDA on I/O P38 defines direction (input=1/output=0) #define SDA_CONF P3H_bit.no0 //SDA level on output direction #define SCL PM3H_bit.no1 //SCL on I/O P39 defines direction (input=1/output=0) #define SCL_CONF P3H_bit.no1 //SCL level on output direction  //---------- Enumerations ------------------------------------------------------ // I2C level typedef enum{ 
           LOW                      = 0,   HIGH                     = 1, }etI2cLevel;  // I2C acknowledge typedef enum{ 
           ACK                      = 0,   NO_ACK                   = 1, }etI2cAck;  //============================================================================== void I2c_Init (); //============================================================================== //Initializes the ports for I2C interface  //============================================================================== void I2c_StartCondition (); //============================================================================== // writes a start condition on I2C-bus // input : - // output: - // return: - // note : timing (delay) may have to be changed for different microcontroller // _____ // SDA: |_____ // _______
// SCL : |___

//==============================================================================
void I2c_StopCondition ();
//==============================================================================
// writes a stop condition on I2C-bus
// input : -
// output: -
// return: -
// note : timing (delay) may have to be changed for different microcontroller
// _____
// SDA: _____|
// _______
// SCL : ___|

//===========================================================================
u8t I2c_WriteByte (u8t txByte);
//===========================================================================
// writes a byte to I2C-bus and checks acknowledge
// input: txByte transmit byte
// output: -
// return: error
// note: timing (delay) may have to be changed for different microcontroller

//===========================================================================
u8t I2c_ReadByte (etI2cAck ack);
//===========================================================================
// reads a byte on I2C-bus
// input: rxByte receive byte
// output: rxByte
// note: timing (delay) may have to be changed for different microcontroller

#endif

I2C.c

//---------- Includes ----------------------------------------------------------
#include "I2C_HAL.h"

//==============================================================================
void I2c_Init ()
//==============================================================================
{ 
        
  SDA=LOW;                // Set port as output for configuration
  SCL=LOW;                // Set port as output for configuration

  SDA_CONF=LOW;           // Set SDA level as low for output mode
  SCL_CONF=LOW;           // Set SCL level as low for output mode

  SDA=HIGH;               // I2C-bus idle mode SDA released (input)
  SCL=HIGH;               // I2C-bus idle mode SCL released (input)
}

//==============================================================================
void I2c_StartCondition ()
//==============================================================================
{ 
        
  SDA=HIGH;
  SCL=HIGH;
  SDA=LOW;
  DelayMicroSeconds(10);  // hold time start condition (t_HD;STA)
  SCL=LOW;
  DelayMicroSeconds(10);
}

//==============================================================================
void I2c_StopCondition ()
//==============================================================================
{ 
        
  SDA=LOW;
  SCL=LOW;
  SCL=HIGH;
  DelayMicroSeconds(10);  // set-up time stop condition (t_SU;STO)
  SDA=HIGH;
  DelayMicroSeconds(10);
}

//==============================================================================
u8t I2c_WriteByte (u8t txByte)
//==============================================================================
{ 
        
  u8t mask,error=0;
  for (mask=0x80; mask>0; mask>>=1)   //shift bit for masking (8 times)
  { 
         if ((mask & txByte) == 0) SDA=LOW;//masking txByte, write bit to SDA-Line
    else SDA=HIGH;
    DelayMicroSeconds(1);             //data set-up time (t_SU;DAT)
    SCL=HIGH;                         //generate clock pulse on SCL
    DelayMicroSeconds(5);             //SCL high time (t_HIGH)
    SCL=LOW;
    DelayMicroSeconds(1);             //data hold time(t_HD;DAT)
  }
  SDA=HIGH;                           //release SDA-line
  SCL=HIGH;                           //clk #9 for ack
  DelayMicroSeconds(1);               //data set-up time (t_SU;DAT)
  if(SDA_CONF==HIGH) error=ACK_ERROR; //check ack from i2c slave
  SCL=LOW;
  DelayMicroSeconds(20);              //wait time to see byte package on scope
  return error;                       //return error code
}

//==============================================================================
u8t I2c_ReadByte (etI2cAck ack)
//==============================================================================
{ 
        
  u8t mask,rxByte=0;
  SDA=HIGH;                           //release SDA-line
  for (mask=0x80; mask>0; mask>>=1)   //shift bit for masking (8 times)
  { 
         SCL=HIGH;                         //start clock on SCL-line
    DelayMicroSeconds(1);             //data set-up time (t_SU;DAT)
    DelayMicroSeconds(3);             //SCL high time (t_HIGH)
    if (SDA_CONF==1) rxByte=(rxByte | mask); //read bit
    SCL=LOW;
    DelayMicroSeconds(1);             //data hold time(t_HD;DAT)
  }
  SDA=ack;                            //send acknowledge if necessary
  DelayMicroSeconds(1);               //data set-up time (t_SU;DAT)
  SCL=HIGH;                           //clk #9 for ack
  DelayMicroSeconds(5);               //SCL high time (t_HIGH)
  SCL=LOW;
  SDA=HIGH;                           //release SDA-line
  DelayMicroSeconds(20);              //wait time to see byte package on scope
  return rxByte;                      //return error code
}

SHT2x.h

#ifndef SHT2x_H
#define SHT2x_H
//---------- Includes ----------------------------------------------------------
#include "I2C.h"
//---------- Defines -----------------------------------------------------------
// CRC
const u16t POLYNOMIAL = 0x131;  //P(x)=x^8+x^5+x^4+1 = 100110001

// sensor command
typedef enum{ 
        
  TRIG_T_MEASUREMENT_HM    = 0xE3, // command trig. temp meas. hold master
  TRIG_RH_MEASUREMENT_HM   = 0xE5, // command trig. humidity meas. hold master
  TRIG_T_MEASUREMENT_POLL  = 0xF3, // command trig. temp meas. no hold master
  TRIG_RH_MEASUREMENT_POLL = 0xF5, // command trig. humidity meas. no hold master
  USER_REG_W               = 0xE6, // command writing user register
  USER_REG_R               = 0xE7, // command reading user register
  SOFT_RESET               = 0xFE  // command soft reset
}etSHT2xCommand;

typedef enum { 
        
  SHT2x_RES_12_14BIT       = 0x00, // RH=12bit, T=14bit
  SHT2x_RES_8_12BIT        = 0x01, // RH= 8bit, T=12bit
  SHT2x_RES_10_13BIT       = 0x80, // RH=10bit, T=13bit
  SHT2x_RES_11_11BIT       = 0x81, // RH=11bit, T=11bit
  SHT2x_RES_MASK           = 0x81  // Mask for res. bits (7,0) in user reg.
} etSHT2xResolution;

typedef enum { 
        
  SHT2x_EOB_ON             = 0x40, // end of battery
  SHT2x_EOB_MASK           = 0x40, // Mask for EOB bit(6) in user reg.
} etSHT2xEob;

typedef enum { 
        
  SHT2x_HEATER_ON          = 0x04, // heater on
  SHT2x_HEATER_OFF         = 0x00, // heater off
  SHT2x_HEATER_MASK        = 0x04, // Mask for Heater bit(2) in user reg.
} etSHT2xHeater;

// measurement signal selection
typedef enum{ 
        
  HUMIDITY,
  TEMP
}etSHT2xMeasureType;

typedef enum{ 
        
  I2C_ADR_W                = 128,   // sensor I2C address + write bit
  I2C_ADR_R                = 129    // sensor I2C address + read bit
}etI2cHeader;




//==============================================================================
u8t SHT2x_CheckCrc(u8t data[], u8t nbrOfBytes, u8t checksum);
//==============================================================================
// calculates checksum for n bytes of data and compares it with expected
// checksum
// input: data[] checksum is built based on this data
// nbrOfBytes checksum is built for n bytes of data
// checksum expected checksum
// return: error: CHECKSUM_ERROR = checksum does not match
// 0 = checksum matches

//==============================================================================
u8t SHT2x_ReadUserRegister(u8t *pRegisterValue);
//==============================================================================
// reads the SHT2x user register (8bit)
// input : -
// output: *pRegisterValue
// return: error

//==============================================================================
u8t SHT2x_WriteUserRegister(u8t *pRegisterValue);
//==============================================================================
// writes the SHT2x user register (8bit)
// input : *pRegisterValue
// output: -
// return: error

//==============================================================================
u8t SHT2x_MeasurePoll(etSHT2xMeasureType eSHT2xMeasureType, nt16 *pMeasurand);
//==============================================================================
// measures humidity or temperature. This function polls every 10ms until
// measurement is ready.
// input: eSHT2xMeasureType
// output: *pMeasurand: humidity / temperature as raw value
// return: error
// note: timing for timeout may be changed

//==============================================================================
u8t SHT2x_MeasureHM(etSHT2xMeasureType eSHT2xMeasureType, nt16 *pMeasurand);
//==============================================================================
// measures humidity or temperature. This function waits for a hold master until
// measurement is ready or a timeout occurred.
// input: eSHT2xMeasureType
// output: *pMeasurand: humidity / temperature as raw value
// return: error
// note: timing for timeout may be changed

//==============================================================================
u8t SHT2x_SoftReset();
//==============================================================================
// performs a reset
// input: -
// output: -
// return: error

//==============================================================================
float SHT2x_CalcRH(u16t u16sRH);
//==============================================================================
// calculates the relative humidity
// input: sRH: humidity raw value (16bit scaled)
// return: pHumidity relative humidity [%RH]

//==============================================================================
float SHT2x_CalcTemperatureC(u16t u16sT);
//==============================================================================
// calculates temperature
// input: sT: temperature raw value (16bit scaled)
// return: temperature [癈]

//==============================================================================
u8t SHT2x_GetSerialNumber(u8t u8SerialNumber[]);
//==============================================================================
// gets serial number of SHT2x according application note "How To
// Read-Out the Serial Number"
// note: readout of this function is not CRC checked
//
// input: -
// output: u8SerialNumber: Array of 8 bytes (64Bits)
// MSB LSB
// u8SerialNumber[7] u8SerialNumber[0]
// SNA_1 SNA_0 SNB_3 SNB_2 SNB_1 SNB_0 SNC_1 SNC_0
// return: error
#endif

SHT2x.c

//---------- Includes ----------------------------------------------------------
#include "SHT2x.h"

//==============================================================================
u8t SHT2x_CheckCrc(u8t data[], u8t nbrOfBytes, u8t checksum)
//==============================================================================
{ 
        
  u8t crc = 0;	
  u8t byteCtr;
  //calculates 8-Bit checksum with given polynomial
  for (byteCtr = 0; byteCtr < nbrOfBytes; ++byteCtr)
  { 
         crc ^= (data[byteCtr]);
    for (u8t bit = 8; bit > 0; --bit)
    { 
         if (crc & 0x80) crc = (crc << 1) ^ POLYNOMIAL;
      else crc = (crc << 1);
    }
  }
  if (crc != checksum) return CHECKSUM_ERROR;
  else return 0;
}

//===========================================================================
u8t SHT2x_ReadUserRegister(u8t *pRegisterValue)
//===========================================================================
{ 
        
  u8t checksum;   //variable for checksum byte
  u8t error=0;    //variable for error code

  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W);
  error |= I2c_WriteByte (USER_REG_R);
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_R);
  *pRegisterValue = I2c_ReadByte(ACK);
  checksum=I2c_ReadByte(NO_ACK);
  error |= SHT2x_CheckCrc (pRegisterValue,1,checksum);
  I2c_StopCondition();
  return error;
}

//===========================================================================
u8t SHT2x_WriteUserRegister(u8t *pRegisterValue)
//===========================================================================
{ 
        
  u8t error=0;   //variable for error code

  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W);
  error |= I2c_WriteByte (USER_REG_W);
  error |= I2c_WriteByte (*pRegisterValue);
  I2c_StopCondition();
  return error;
}

//===========================================================================
u8t SHT2x_MeasureHM(etSHT2xMeasureType eSHT2xMeasureType, nt16 *pMeasurand)
//===========================================================================
{ 
        
  u8t  checksum;   //checksum
  u8t  data[2];    //data array for checksum verification
  u8t  error=0;    //error variable
  u16t i;          //counting variable

  //-- write I2C sensor address and command --
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W); // I2C Adr
  switch(eSHT2xMeasureType)
  { 
         case HUMIDITY: error |= I2c_WriteByte (TRIG_RH_MEASUREMENT_HM); break;
    case TEMP    : error |= I2c_WriteByte (TRIG_T_MEASUREMENT_HM);  break;
    default: assert(0);
  }
  //-- wait until hold master is released --
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_R);
  SCL=HIGH;                     // set SCL I/O port as input
  for(i=0; i<1000; i++)         // wait until master hold is released or
  { 
         DelayMicroSeconds(1000);    // a timeout (~1s) is reached
    if (SCL_CONF==1) break;
  }
  //-- check for timeout --
  if(SCL_CONF==0) error |= TIME_OUT_ERROR;

  //-- read two data bytes and one checksum byte --
  pMeasurand->s16.u8H = data[0] = I2c_ReadByte(ACK);
  pMeasurand->s16.u8L = data[1] = I2c_ReadByte(ACK);
  checksum=I2c_ReadByte(NO_ACK);

  //-- verify checksum --
  error |= SHT2x_CheckCrc (data,2,checksum);
  I2c_StopCondition();
  return error;
}

//===========================================================================
u8t SHT2x_MeasurePoll(etSHT2xMeasureType eSHT2xMeasureType, nt16 *pMeasurand)
//===========================================================================
{ 
        
  u8t  checksum;   //checksum
  u8t  data[2];    //data array for checksum verification
  u8t  error=0;    //error variable
  u16t i=0;        //counting variable

  //-- write I2C sensor address and command --
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W); // I2C Adr
  switch(eSHT2xMeasureType)
  { 
         case HUMIDITY: error |= I2c_WriteByte (TRIG_RH_MEASUREMENT_POLL); break;
    case TEMP    : error |= I2c_WriteByte (TRIG_T_MEASUREMENT_POLL);  break;
    default: assert(0);
  }
  //-- poll every 10ms for measurement ready. Timeout after 20 retries (200ms)--
  do
  { 
         I2c_StartCondition();
    DelayMicroSeconds(10000);  //delay 10ms
    if(i++ >= 20) break;
  } while(I2c_WriteByte (I2C_ADR_R) == ACK_ERROR);
  if (i>=20) error |= TIME_OUT_ERROR;

  //-- read two data bytes and one checksum byte --
  pMeasurand->s16.u8H = data[0] = I2c_ReadByte(ACK);
  pMeasurand->s16.u8L = data[1] = I2c_ReadByte(ACK);
  checksum=I2c_ReadByte(NO_ACK);

  //-- verify checksum --
  error |= SHT2x_CheckCrc (data,2,checksum);
  I2c_StopCondition();

  return error;
}

//===========================================================================
u8t SHT2x_SoftReset()
//===========================================================================
{ 
        
  u8t  error=0;           //error variable

  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W); // I2C Adr
  error |= I2c_WriteByte (SOFT_RESET);                            // Command
  I2c_StopCondition();

  DelayMicroSeconds(15000); // wait till sensor has restarted

  return error;
}

//==============================================================================
float SHT2x_CalcRH(u16t u16sRH)
//==============================================================================
{ 
        
  ft humidityRH;              // variable for result

  u16sRH &= ~0x0003;          // clear bits [1..0] (status bits)
  //-- calculate relative humidity [%RH] --

  humidityRH = -6.0 + 125.0/65536 * (ft)u16sRH; // RH= -6 + 125 * SRH/2^16
  return humidityRH;
}

//==============================================================================
float SHT2x_CalcTemperatureC(u16t u16sT)
//==============================================================================
{ 
        
  ft temperatureC;            // variable for result

  u16sT &= ~0x0003;           // clear bits [1..0] (status bits)

  //-- calculate temperature [癈] --
  temperatureC= -46.85 + 175.72/65536 *(ft)u16sT; //T= -46.85 + 175.72 * ST/2^16
  return temperatureC;
}

//==============================================================================
u8t SHT2x_GetSerialNumber(u8t u8SerialNumber[])
//==============================================================================
{ 
        
  u8t  error=0;                          //error variable

  //Read from memory location 1
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W);    //I2C address
  error |= I2c_WriteByte (0xFA);         //Command for readout on-chip memory
  error |= I2c_WriteByte (0x0F);         //on-chip memory address
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_R);    //I2C address
  u8SerialNumber[5] = I2c_ReadByte(ACK); //Read SNB_3
  I2c_ReadByte(ACK);                     //Read CRC SNB_3 (CRC is not analyzed)
  u8SerialNumber[4] = I2c_ReadByte(ACK); //Read SNB_2
  I2c_ReadByte(ACK);                     //Read CRC SNB_2 (CRC is not analyzed)
  u8SerialNumber[3] = I2c_ReadByte(ACK); //Read SNB_1
  I2c_ReadByte(ACK);                     //Read CRC SNB_1 (CRC is not analyzed)
  u8SerialNumber[2] = I2c_ReadByte(ACK); //Read SNB_0
  I2c_ReadByte(NO_ACK);                  //Read CRC SNB_0 (CRC is not analyzed)
  I2c_StopCondition();

  //Read from memory location 2
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_W);    //I2C address
  error |= I2c_WriteByte (0xFC);         //Command for readout on-chip memory
  error |= I2c_WriteByte (0xC9);         //on-chip memory address
  I2c_StartCondition();
  error |= I2c_WriteByte (I2C_ADR_R);    //I2C address
  u8SerialNumber[1] = I2c_ReadByte(ACK); //Read SNC_1
  u8SerialNumber[0] = I2c_ReadByte(ACK); //Read SNC_0
  I2c_ReadByte(ACK);                     //Read CRC SNC0/1 (CRC is not analyzed)
  u8SerialNumber[7] = I2c_ReadByte(ACK); //Read SNA_1
  u8SerialNumber[6] = I2c_ReadByte(ACK); //Read SNA_0
  I2c_ReadByte(NO_ACK);                  //Read CRC SNA0/1 (CRC is not analyzed)
  I2c_StopCondition();

  return error;
}