SPI Loopback using USCI MSP430G2553

[lunix 0]

Hi all,

 

I'm trying to do a loopback code on the MSP430G2553 chip.

 

It's supposed to turn the red light off whenever the SPI UCA0 receives the character "A" transmitted from the master SPI UCB0.

 

#include "msp430g2553.h"
#include 

void main(void) {
 WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer

 P1DIR |= BIT0;
 P1OUT |= BIT0;

 P1SEL = BIT1 + BIT2 + BIT4;
 P1SEL2 = BIT1 + BIT2 + BIT4;
 UCA0CTL1 = UCSWRST;                       // **Put state machine in reset**
 UCA0CTL0 |= UCCKPL + UCMSB + UCSYNC;      // 3-pin, 8-bit SPI slave
 UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
 IE2 |= UCA0RXIE;                          // Enable USCI0 RX interrupt

 // Slave setup done
 ///////////////////////////////////////////////////////////////////////


 P1SEL = BIT5 + BIT6 + BIT7;
 P1SEL2 = BIT5 + BIT6 + BIT7;
 UCB0CTL0 |= UCCKPL + UCMSB + UCMST + UCSYNC;  // 3-pin, 8-bit SPI master
 UCB0CTL1 |= UCSSEL_2;                     // SMCLK
 UCB0BR0 |= 0x02;                          // /2
 UCB0BR1 = 0;                              //
 //UCB0MCTL = 0;                             // No modulation
 UCB0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
 IE2 |= UCB0TXIE;                          // Enable USCI0 TX interrupt

 while(1) {
   __bis_SR_register(LPM0_bits + GIE);       // Enter LPM4, enable interrupts
 }
}

interrupt(USCIAB0RX_VECTOR) USCI0RX_ISR(void) {
 if (UCA0RXBUF == 'A') {
     P1OUT &= ~BIT0;
 }
}

interrupt(USCIAB0TX_VECTOR) USCI0TX_ISR(void) {
   UCB0TXBUF = 'A';                     // Transmit first character
}

 

I conneced pin 1.4 to pin 1.5, pin 1.2 to pin 1.7, pin 1.6 to pin 1.1. The jumper P1.6 on the launchpad board is disconnected with the LED.

 

I seems like the code should work but it never does -- the red light stays on. Anyone would help me figure out why it's the case?

[lunix 0]

Nevermind, got it to work, all I changed was to set up pin directions at the beginning.

 

#include "msp430g2553.h"
#include 

void transfer(char s) {
   while (!(IFG2 & UCB0TXIFG));
   UCB0TXBUF = s;
}

void main(void) {
 WDTCTL = WDTPW + WDTHOLD;                 // Stop watchdog timer

 P1DIR |= BIT0;
 P1OUT |= BIT0;

 P1SEL = BIT1 + BIT2 + BIT4 + BIT5 + BIT6 + BIT7;
 P1SEL2 = BIT1 + BIT2 + BIT4 + BIT5 + BIT6 + BIT7;

 UCA0CTL1 = UCSWRST;                       // **Put state machine in reset**
 UCA0CTL0 |= UCCKPL + UCMSB + UCSYNC;      // 3-pin, 8-bit SPI slave
 UCA0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**

 while(IFG2 & UCA0RXIFG);

 IE2 |= UCA0RXIE;                          // Enable USCI0 RX interrupt

 // Slave setup done
 ///////////////////////////////////////////////////////////////////////
 __delay_cycles(60000);
 __delay_cycles(60000);
 __delay_cycles(60000);
 __delay_cycles(60000);

 UCB0CTL0 |= UCCKPL + UCMSB + UCMST + UCSYNC;  // 3-pin, 8-bit SPI master
 UCB0CTL1 |= UCSSEL_2;                     // SMCLK
 UCB0BR0 |= 0x02;                          // /2
 UCB0BR1 = 0;                              //
 //UCB0MCTL = 0;                             // No modulation
 UCB0CTL1 &= ~UCSWRST;                     // **Initialize USCI state machine**
 IE2 |= UCB0TXIE;                          // Enable USCI0 TX interrupt

 //transfer('A');

 while(1) {
   __bis_SR_register(LPM4_bits + GIE);       // Enter LPM4, enable interrupts
 }
}

// Echo character
interrupt(USCIAB0RX_VECTOR) USCI0RX_ISR(void) {
 //while (!(IFG2 & UCA0TXIFG));              // USCI_A0 TX buffer ready?
 if (UCA0RXBUF == 'A') {
   P1OUT &= ~BIT0;
 }
}

interrupt(USCIAB0TX_VECTOR) USCI0TX_ISR(void) {
   UCB0TXBUF = 'A';                     // Transmit first character
}

[fatihinanc 14]

You can use debugger for like this things.

Would you try, add to watch window the UCB0RXBUF ?

This way, might be possible to find the problem as quickly.

[bluehash 1,581]

Red Lobster reporting, I see.