SPI Transfer Issue

whata — Mon, 02 Nov 2020 13:57:05 GMT

Hi,

I'm attempting to communicate with an external adc (LTC1864L) , but the results that I'm reading back are wrong. My spi setup is as follows:

    /* Configure the spi module
     * SCK synchronizes the data transfer with each bit
     * being transmitted from SDO on the falling SCK edge.
     * The receiving system should capture the data from
     * SDO on the rising edge of SCK
     */
    sensor->cfg.whichCtar = kDSPI_Ctar0;
    sensor->cfg.ctarConfig.baudRate = SPI_BAUDRATE;
    sensor->cfg.ctarConfig.bitsPerFrame = 16U;
    sensor->cfg.ctarConfig.cpol = kDSPI_ClockPolarityActiveLow;
    sensor->cfg.ctarConfig.cpha = kDSPI_ClockPhaseFirstEdge;
    sensor->cfg.ctarConfig.direction = kDSPI_MsbFirst;
    sensor->cfg.ctarConfig.pcsToSckDelayInNanoSec = 1000000000U / SPI_BAUDRATE;
    sensor->cfg.ctarConfig.lastSckToPcsDelayInNanoSec = 1000000000U / SPI_BAUDRATE;
    sensor->cfg.ctarConfig.betweenTransferDelayInNanoSec = 1000000000U / SPI_BAUDRATE;

    sensor->cfg.whichPcs = kDSPI_Pcs0;
    sensor->cfg.pcsActiveHighOrLow = kDSPI_PcsActiveLow;

    sensor->cfg.enableContinuousSCK = false;
    sensor->cfg.enableRxFifoOverWrite = true;
    sensor->cfg.enableModifiedTimingFormat = false;
    sensor->cfg.samplePoint = kDSPI_SckToSin2Clock;

    DSPI_MasterInit(SPI1, &sensor->cfg, CLOCK_GetFreq(DSPI1_CLK_SRC));‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍‍

Baudrate is set to 500k. The transfer is initialized as follows (SPI_TXSIZE = 2):

    /* Clear buffer */
    sensor->rxData[0] = 0;
    sensor->rxData[1] = 0;

    /* Start master transfer */
    sensor->xfer.txData = sensor->txData;
    sensor->xfer.rxData = sensor->rxData;
    sensor->xfer.dataSize = SPI_TXSIZE;
    sensor->xfer.configFlags = kDSPI_MasterCtar0 | kDSPI_MasterPcs0 | kDSPI_MasterPcsContinuous;

    DSPI_MasterTransferCreateHandle (SPI1, &g_m_handle, SENSOR_MasterCb, NULL);
    DSPI_MasterTransferNonBlocking (SPI1, &g_m_handle, &sensor->xfer);‍‍‍‍‍‍‍‍‍‍‍‍

The scope shows the following image:

While the rxData contains 0x12, 0x00 which is clearly wrong. Is there something that I'm missing?

Re: SPI Transfer Issue

Hui_Ma — Wed, 31 May 2017 06:46:29 GMT

Hi ,

I checked the LTC1864L datasheet, the SPI output data with MSB first:

So, the data you get is 0x0018.

Have a great day,
Ma Hui

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