MSP430G2553 I2C problem on while (UCB0CTL1 & UCTXSTT){ }

Lubomir Bogdanov

Other Parts Discussed in Thread: MSP430G2553

Hello!

I've deliberately named my question like that - I know that it's already been asked but the answers don't help me at all.

I have a custom board with MSP430G2553 and an I2C real-time clock M41T81S. I program it through the MSP-EXP430G2 launch pad. I use TEST & RST (pin 16, 17) & GND for programming. I have NO pull-ups. I use the internal ones. I use external Vdd.

My communication is stuck at while(UCB0CTL1 & UCTXSTT){ } and doesn't go on. Can please someone give me any ideas? Here's the code:

#include <msp430.h>

int main(void)
{
  WDTCTL = WDTPW + WDTHOLD; 

  // Set DCO to 16MHz
  BCSCTL1 = CALBC1_16MHZ;
  DCOCTL = CALDCO_16MHZ;
  
  BCSCTL2 &= ~SELS; //SMCLK = DCOCLK
  
  P1SEL |= 0xC0;
  P1SEL2|= 0xC0;                     		
  P1REN |= 0xC0;
  P1OUT |= 0xC0;

  UCB0CTL1 |= UCSWRST;

  UCB0CTL0 = UCMST+UCMODE_3+UCSYNC;
  UCB0CTL1 = UCSSEL_2+UCSWRST;  
  UCB0BR0 = 160;    // fSCL = SMCLK/160 = ~100kbps
  UCB0BR1 = 0;
  UCB0I2CSA = 0x68;                        

  UCB0CTL1 &= ~UCSWRST;                     

  while (1)
  {
	UCB0CTL1 |= UCTR;                		
	UCB0CTL1 |= UCTXSTT;             		
	while (UCB0CTL1 & UCTXSTT){ }    		

	UCB0TXBUF = 0x02;
	while(IFG2 & UCB0TXIFG){ }

        UCB0CTL1 |= UCTXSTP;      
        while (UCB0CTL1 & UCTXSTT){ }
  }
}


Thanks in advance!

over 11 years ago

0 Lubomir Bogdanov over 11 years ago

Prodigy 40 points

I got it working finally! IF YOU PLAN to use the polling method for I2C I advice you to do the following:

- Before the transmission is started wait a huge amount of time because the slave IC might not initialize as fast as the MCU

- When you develop your I2C code POWER-CYCLE the board because the slave I2C may crash and hold the lines low or something like that (during the programming of the MSP430 the I2C lines are sometimes toggling!)

- DO NOT use the internal pull-ups when using the I2C module ... solder external pull-ups (in my case - 3k3)

- DO NOT wait for the UCTXSTT bit to be cleared. Use the UCB0TXIFG flag instead.

Here is my working code:

#include <msp430.h>

int main(void)
{
  WDTCTL = WDTPW + WDTHOLD;                 // Stop Watchdog Timer

  // Set DCO to 16MHz
  BCSCTL1 = CALBC1_16MHZ;
  DCOCTL = CALDCO_16MHZ;
  //SMCLK = DCOCLK
  BCSCTL2 &= ~SELS;
  
  P1SEL |= 0xC0;                     		// Assign I2C pins to USCI_B0
  P1SEL2|= 0xC0;                     		// Assign I2C pins to USCI_B0
  //P1REN |= 0xC0; //DO NOT USE
  //P1OUT |= 0xC0; //DO NOT USE

  UCB0CTL1 |= UCSWRST;                      // Enable SW reset

  UCB0CTL0 = UCMST | UCMODE_3 | UCSYNC;     // I2C Master, synchronous mode
  UCB0CTL1 |= UCSSEL_2;              		// Use SMCLK
  UCB0BR0 = 160;                            // fSCL = SMCLK/160 = ~100kbps
  UCB0BR1 = 0;
  UCB0I2CSA = 0x68;                         // Set slave address
  IFG2 &= ~UCB0TXIFG;

  UCB0CTL1 &= ~UCSWRST;                     // Clear SW reset, resume operation

  __delay_cycles(500000); //Wait for slave to initialize

  while (1)
  {
	while (UCB0CTL1 & UCTXSTP);
	UCB0CTL1 |= UCTR + UCTXSTT;
	//while (UCB0CTL1 & UCTXSTT); //DO NOT USE
	while(!(IFG2 & UCB0TXIFG)){ }
	IFG2 &= ~UCB0TXIFG;
	UCB0TXBUF = 0x02;
	while(!(IFG2 & UCB0TXIFG)){ }
	IFG2 &= ~UCB0TXIFG;
	UCB0CTL1 |= UCTXSTP;
  }
}

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MSP430G2553 I2C problem on while (UCB0CTL1 & UCTXSTT){ }