i2c_master.c

MSP430F2350 I2C Library

#include "io430.h"               
#include "in430.h"
#include "I2C_master.h"

unsigned char byteCtr;                        // byte number control
unsigned char *receive_field;                 // pointer to the store
unsigned char *transmit_field;                // pointer to the data

//initialize clock
void I2C_Clock(void)
{
  BCSCTL1 |= XTS;                             // ACLK = LFXT1 = HF XTAL
  BCSCTL3 |= LFXT1S1;                         // 3 ?16MHz crystal or resonator
  do
  {
    IFG1 &= ~OFIFG;                           // Clear OSCFault flag
    for (unsigned char i = 0xFF; i > 0; i--); // Time for flag to set
  }
  while (IFG1 & OFIFG);                       // OSCFault flag still set?
  BCSCTL2 |= SELM_3 + SELS;                   // MCLK = SMCLK = LFXT1=7.3728MHz
}

//initialize I2C communication
void I2C_Init(unsigned char slave_address, unsigned char prescale)
{
  P3SEL |= SDA_PIN + SCL_PIN;                 // select I2C module
  UCB0CTL1 = UCSWRST;                         // enable SW reset => STOP
  UCB0CTL0 = UCMST + UCMODE_3 + UCSYNC;       // Master + I2C + Synchronous
  UCB0CTL1 = UCSSEL_2 + UCSWRST;              // set BRCLK = SMCLK + SW reset
  UCB0BR0 = prescale;                         // set lower byte of prescale
  UCB0BR1 = 0;                                // set higher byte of prescale
  UCB0I2CSA = slave_address;                  // set slave address
  UCB0CTL1 &= ~UCSWRST;                       // clear SW reset => RESUME
  UCB0I2CIE = UCNACKIE;                       // enable NACK interrupt  
}

//initialize I2C receive 
void I2C_Receive_Init(unsigned char slave_address, unsigned char prescale)
{
  I2C_Init(slave_address,prescale);           // initial basic I2C parameters
  IE2 = UCB0RXIE;                             // enable RX interrupt
}

//initialize I2C transmit
void I2C_Transmit_Init(unsigned char slave_address, unsigned char prescale)
{
  I2C_Init(slave_address,prescale);           // initial basic I2C parameters
  IE2 = UCB0TXIE;                             // enable TX interrupt
}

//start I2C receive
void I2C_Receive(unsigned char byteCount, unsigned char *field)
{
  receive_field = field;  
  if ( byteCount == 1 )                       // receive 1 byte
  {
    byteCtr = 0 ;                             // 0 remaining byte
    _DINT();                                  // disable GIE
    UCB0CTL1 |= UCTXSTT;                      // send start and address
    while (UCB0CTL1 & UCTXSTT);               // check start sent
    UCB0CTL1 |= UCTXSTP;                      // send stop
    _EINT();                                  // enable GIE
  }   
  else                                        // receive more than 1 byte
  {
    byteCtr = byteCount - 2;                  // total - 2 remaining byte due to byte receive first than interrupt
    UCB0CTL1 |= UCTXSTT;                      // send start and address
  }
}

//start I2C transmit
void I2C_Transmit(unsigned char byteCount, unsigned char *field)
{
  transmit_field = field;                     // pass the address
  byteCtr = byteCount;                        // pass the send count
  UCB0CTL1 |= UCTR + UCTXSTT;                 // I2C transmiter + send start and address
}

//check the finish of communication
void I2C_Not_Ready(void)
{
  while (UCB0STAT & UCBBUSY);                 //loop when unfinish
}

// the interrupt vector of I2C state change of USCI_B0
#pragma vector = USCIAB0RX_VECTOR             
__interrupt void USCIAB0RX_ISR(void)          
{
  if (UCB0STAT & UCNACKIFG)                   // check NACK
  {            
    UCB0CTL1 |= UCTXSTP;                      // send stop
    UCB0STAT &= ~UCNACKIFG;                   // clear NACK flag
  }
}

// the interrupt vector of both receive and transmit of USCI_B0 I2C
#pragma vector = USCIAB0TX_VECTOR 
__interrupt void USCIAB0TX_ISR(void)
{  
  if (IFG2 & UCB0RXIFG)                       // check I2C receive 
  {    
    if ( byteCtr == 0 )                       // remain 1 byte
    {
      UCB0CTL1 |= UCTXSTP;                    // send stop 
      *receive_field = UCB0RXBUF;             // store received
      receive_field++;                        // point to next store
    }        
    else                                      // remain more bytes
    {               
      *receive_field = UCB0RXBUF;             // store received
      receive_field++;                        // point to next store
      byteCtr--;                              // minus the total receive count
    }    
  }  
  if (IFG2 & UCB0TXIFG)                       // check I2C transmit
  {    
    if (byteCtr == 0)                         // no more bytes
    {
      UCB0CTL1 |= UCTXSTP;                    // send stop
      IFG2 &= ~UCB0TXIFG;                     // clear TX flag
    }        
    else                                      // remain more than 1 bytes
    {
      UCB0TXBUF = *transmit_field;            // send data
      transmit_field++;                       // point to next byte
      byteCtr--;                              // minus the total send count
    }    
  }   
}