I2C communication on msp430f5438 experiment board

Other Parts Discussed in Thread: MSP430F5438

Hi,

I am trying to test the I2C communication on the msp430f5438 experiment board

I noticed there are 4 I2C module, USCI_B0 to USCI_B3. and it looks like only USCI_B1 and USCI_B3 are available on general pins. (USCI_B1 is available on pin3.7 and pin5.4;  USCI_B3 is available on pin10.1 and pin10.2)

what i did is configure B3 as master transmitter to transmit a single byte that will be received on USCI_B1 as a slave receiver.

I set 2 breakpoints respectively at transmitter interrupt and receiver interrupt to observe if the data is transmitted and received successfully.

the following is the source code

#include <msp430.h> 

/*
 * main.c
 */

unsigned char TXData;
unsigned char TXByteCtr;
volatile unsigned char RXData;

int main(void) {
    WDTCTL = WDTPW | WDTHOLD;	// Stop watchdog timer
	P1DIR |= BIT0;
	P1OUT &= ~BIT0;
	/* initialize UCB3 */
    P10SEL |= BIT1 + BIT2;
    P10DIR |= BIT1 + BIT2;
    UCB3CTL1 |= UCSWRST;
    UCB3CTL0 |= UCMST + UCMODE_3 + UCSYNC;
    UCB3CTL1 |= UCSSEL_2 + UCSWRST;

    UCB3BR0 = 12;
    UCB3BR1 = 0;
    UCB3I2CSA = 0x48;
    UCB3CTL1 &= ~UCSWRST;
    UCB3IE |= UCTXIE;

    TXData = 0x01;

    /* initialize UCB1 */
    P3DIR &= ~BIT7;
    P3SEL |= BIT7;
    P5OUT &= ~BIT4;
    P5SEL |= BIT4;

    UCB1CTL1 |= UCSWRST;

    UCB1CTL0 |= UCMODE_3 + UCSYNC;

    UCB1I2COA = 0x48;
    UCB1CTL1 &= ~UCSWRST;

    UCB1IE |= UCRXIE;

    while(1){
    	TXByteCtr = 1;

    	while(UCB3CTL1 & UCTXSTP);

    	UCB3CTL1 |= UCTR + UCTXSTT;

    	__bis_SR_register(LPM0_bits + GIE);
    	__no_operation();

    	TXData++;
    }
}

#pragma vector = USCI_B3_VECTOR

__interrupt void USCI_B3_ISR(void){

	switch(UCB3IV){

	case 12:
		if(TXByteCtr){
			UCB3TXBUF = TXData;
			TXByteCtr--;
		}
		else{
			UCB3CTL1 |= UCTXSTP;
			UCB3IFG &= ~UCTXIFG;
			__bic_SR_register_on_exit(LPM0_bits);
		}
		break;

	default: break;
	}
}

#pragma vector = USCI_B1_VECTOR

__interrupt void USCI_B1_ISR(void){
	switch(UCB1IV){

	case 10:
		RXData = UCB1RXBUF;
		P1OUT = RXData;
		break;

	default: break;
	}
}

when the program halts at transmitter interrupt, i observed the transmitter NACKIFG is set. it looks like the slave doesn't acknowledge the address transmission.

and both transmitter and receive busy flag is set as well.

when i resume the program, it would not halt at receiver interrupt breakpoint and nothing happens.

can somebody find the error in the code?  or is it a mistake to test 2 I2C bus on the same board?

any suggestion will be appreciated 

Jensen