MSP430FR5969 + SN74AVC4T774 SPI issue

Other Parts Discussed in Thread: SN74AVC4T774, MSP430FR5969

Hi,

I'm currently trying to set up communication between a MSP430FR5969 (LaunchPad) and an Intel Edison through SPI. I've set up a SN74AVC4T774 bus transceiver so I can interface the different voltage levels in each device.

Test code was made with DriverLib's SPI functions. Intel Edison's test code sends a stream of bytes from 1 to 150.

Control signals from the Intel Edison (SPI master) seems to be working fine, but the MSP430 is transmitting on the MISO line with a high level of ~1.2 V, even though it supplies ~3.2 V. Sometimes I even get the bytes looped back, as if MISO and MOSI were shorted, although the MSP430 is programmed to always send 0xFF.

#include "driverlib.h"
#include "stdio.h"

void m_setupSPI(){
	// Set SPI pins
	GPIO_setAsPeripheralModuleFunctionInputPin(GPIO_PORT_P2, GPIO_PIN3 + GPIO_PIN4 + GPIO_PIN5, GPIO_SECONDARY_MODULE_FUNCTION);
	GPIO_setAsPeripheralModuleFunctionOutputPin(GPIO_PORT_P2, GPIO_PIN6, GPIO_SECONDARY_MODULE_FUNCTION);
	// Set SPI mode
	EUSCI_A_SPI_initSlaveParam param = {0};
	param.msbFirst = EUSCI_A_SPI_LSB_FIRST;
	param.clockPhase = EUSCI_A_SPI_PHASE_DATA_CHANGED_ONFIRST_CAPTURED_ON_NEXT;
	param.clockPolarity = EUSCI_A_SPI_CLOCKPOLARITY_INACTIVITY_LOW;
	param.spiMode = EUSCI_A_SPI_4PIN_UCxSTE_ACTIVE_LOW;

	// Enable SPI
	EUSCI_A_SPI_initSlave(EUSCI_A1_BASE, &param);
	EUSCI_A_SPI_enable(EUSCI_A1_BASE);

	// Clear and enable SPI receive interrupt flag
	EUSCI_A_SPI_clearInterrupt(EUSCI_A1_BASE, EUSCI_A_SPI_RECEIVE_INTERRUPT);
	EUSCI_A_SPI_enableInterrupt(EUSCI_A1_BASE, EUSCI_A_SPI_RECEIVE_INTERRUPT);

	// Clear and enable SPI transmit interrupt flag
//	EUSCI_A_SPI_clearInterrupt(EUSCI_A1_BASE, EUSCI_A_SPI_TRANSMIT_INTERRUPT);
//	EUSCI_A_SPI_enableInterrupt(EUSCI_A1_BASE, EUSCI_A_SPI_TRANSMIT_INTERRUPT);
}

int main(void){

//	m_setupSPI();
	GPIO_setAsOutputPin(GPIO_PORT_P2, GPIO_PIN6);
	PMM_unlockLPM5();
	while(1){
//		GPIO_setOutputLowOnPin(GPIO_PORT_P2, GPIO_PIN6);
		GPIO_setOutputHighOnPin(GPIO_PORT_P2, GPIO_PIN6);
//		EUSCI_A_SPI_transmitData(EUSCI_A1_BASE, 0xFF);
	}
}

// This is the SPI serial communication vector of interrupt service routines
#pragma vector=USCI_A1_VECTOR
__interrupt void USCI_A1_ISR(void)
{
    switch(__even_in_range(UCA1IV,4)){
    case USCI_NONE:
    	break;
    case 2:
//    	EUSCI_A_SPI_transmitData(EUSCI_A1_BASE, 0xFF);
    	break;
    }
}

Commented out functions are some of the other tests I've made. The one implemented above gives me the correct output (255).

I'm pretty sure I'm missing something very simple here.