TMS320F28069: SPI loopback occurring even though disabled

Hi,

I'm running into a problem where the SPIRXBUF reads out whatever is in the SPITXBUF. If the loopback function was turned on, I'd expect this -- but I have it turned off.

Here's my SPI transmission function.

void spiTxRx(uint8_t * pau8_txData,
                     uint8_t * pau8_rxData,
                     uint8_t u8_numBytes,
                     uint8_t u8_spiModule,
                     uint8_t u8_chipSelect)
{
     changeCS(u8_chipSelect, CHIP_SELECT_LOW); //set chip select low
     uint8_t u8_i = 0;
     if (u8_spiModule == SPI_MODULE_A_TX)
     {
          for (u8_i = 0; u8_i<u8_numBytes; u8_i++)
          {
               SpiaRegs.SPITXBUF= *(pau8_txData + u8_i);
               // Wait until data is received
               while(SpiaRegs.SPIFFRX.bit.RXFFST !=1) { }
               *(pau8_rxData + u8_i) = (SpiaRegs.SPIRXBUF) >> 8;
          }
     }
     if (u8_spiModule == SPI_MODULE_B_TX)
     {
          for (u8_i = 0; u8_i<u8_numBytes; u8_i++)
          {
               SpibRegs.SPITXBUF= *(pau8_txData + u8_i);
               // Wait until data is received
               while(SpibRegs.SPIFFRX.bit.RXFFST !=1) { }
               // Check against sent data
               *(pau8_rxData + u8_i) = SpibRegs.SPIRXBUF;
          }
     }
     changeCS(u8_chipSelect, CHIP_SELECT_HIGH); //raise chip select now that we're done transmitting
     return;

}

I've attached a screenshot of the SPI B registers that shows the loopback when I'm transmitting SPI. From SPICCR, you can see that bit 4 is 0, so the loopback is disabled.

I've tested this out on both A and B SPI ports on both a dev board (LAUNCHXL-F28069) and a custom PCB with the TMS320F28069 on it and got the same results.

Thanks in advance,

Karen