TMS320F28335: F28335 MAX31856 SPI

GangIn Shin

Prodigy 20 points

Part Number: TMS320F28335

I am trying to do SPI communication with MAX31856 (temperature measurement) using TMS320F28335.

0x0c is transmitted in the first byte
Transmit the remaining 3 bytes 0x00.

The problem is that the values received are not constant and are displayed as 254 or 255.

In my opinion, I think that communication is going on. (It may not be.)

Also, I think there is nothing wrong with the hardware connection.

Below is the code I wrote, I think there is an error in the received value.

What could be causing this?

Thanks for your help.

while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG);
    TxData[0]=0x0c;
    SpiaRegs.SPITXBUF = (TxData[0]<<8);

    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG);
    TxData[1]=0x00; //dummy byte
    SpiaRegs.SPITXBUF = TxData[1];

    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG);
    TxData[2]=0x00;
    SpiaRegs.SPITXBUF = TxData[2];

    while(SpiaRegs.SPISTS.bit.BUFFULL_FLAG);
    TxData[3]=0x00;
    SpiaRegs.SPITXBUF = TxData[3];

    for(i=0;i<4;i++)
    {
        RxData[i] = SpiaRegs.SPIRXBUF;
    }

over 3 years ago

0 Veena Kamath over 3 years ago

TI__Mastermind 32385 points

Hi,

Have you enabled RX FIFO?

Are you saying that the MAX31856 device is successfully sending the data, but the RXDAT contents are incorrect?

Regards,

Veena

0 GangIn Shin over 3 years ago in reply to Veena Kamath

Prodigy 20 points

Hello.

I did not enable RX fifo.

I think that it is normally sent from TX, but I think that the RX value cannot be read normally.

Should I implement Fifo?

Thank you for answer.

0 Veena Kamath over 3 years ago in reply to GangIn Shin

TI__Mastermind 32385 points

Hi,

Since I see you reading from RXBUF back to back, hence asked.

If you are not using RX FIFO, you need to read the data after every transfer, else the RXBUF contents will be replaced by the new data.

Regards,

Veena

0 GangIn Shin over 3 years ago in reply to Veena Kamath

Prodigy 20 points

Hi,

I got the same result in non-FIFO mode.

There is no change to the Rx value.

Do I need to set a flag?

Thanks for your reply.

+1 Veena Kamath over 3 years ago in reply to GangIn Shin

TI__Mastermind 32385 points

Hi,

Are you reading RX DATA after every TX?

Eg:

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    for(;;)
    {
        //
        // Transmit data
        //
        SpiaRegs.SPITXBUF = sData;
        //
        // Wait until data is received
        //
        while(SpiaRegs.SPIFFRX.bit.RXFFST != 1)
        {
        }
        //
        // Check against sent data
        //
        rdata = SpiaRegs.SPIRXBUF;
        if(rdata != sdata)
        {
XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX

    for(;;)
    {
        //
        // Transmit data
        //
        SpiaRegs.SPITXBUF = sData;

        //
        // Wait until data is received
        //
        while(SpiaRegs.SPIFFRX.bit.RXFFST != 1)
        {

        }

        //
        // Check against sent data
        //
        rdata = SpiaRegs.SPIRXBUF;
        if(rdata != sdata)
        {
            error();
        }
        sdata++;

Have you checked the data coming out of MAX31856 (using a scope or logic analyzer)? Is it sending the data as expected?

Regards,

Veena

0 GangIn Shin over 3 years ago in reply to Veena Kamath

Prodigy 20 points

Hello

The current temperature value is being output.
The problem is that I have to reconnect the mosi pin to receive the temperature value. Is it a problem with the max31856 chip?

Also, can I use multiple the address register ?

Thanks for your reply.

0 Veena Kamath over 3 years ago in reply to GangIn Shin

TI__Mastermind 32385 points

Hi,

If the pins are accessible, you can use an oscilloscope/ logic analyzer to monitor if the data is send by the MAX31856 chip or not

GangIn Shin said:
Also, can I use multiple the address register ?

I did not get this question. Is this something specific to MAX31856?

Regards,

Veena

0 GangIn Shin over 3 years ago in reply to Veena Kamath

Prodigy 20 points

Yes for the MAX31856.

Sorry, but I have one question.
Is it possible to delay the clock while the CS pin is held LOW?

thank you for the reply.

0 Veena Kamath over 3 years ago in reply to GangIn Shin

TI__Mastermind 32385 points

You can drive the CS pin via software. To do this, configure the the pin as GPIO and use GPIO registers to drive the pin high/low

Regards,

Veena

0 GangIn Shin over 3 years ago in reply to Veena Kamath

Prodigy 20 points

Thank you for answer.

GpioDataRegs.GPBMUX2.bit.GPIO57 =0; After setting to

GpioDataRegs.GPBCLEAR.bit.GPIO57=1; as
I checked after the change, but there is no change in the CS pin in the High state.

Is there something wrong with my code?

0 Veena Kamath over 3 years ago in reply to GangIn Shin

TI__Mastermind 32385 points

Hi,

You meant GpioCtrlRegs.GPBMUX2, right? Have you enabled EALLOW before this write? You can check the actual value in the Registers view

Regards,

Veena

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TMS320F28335: F28335 MAX31856 SPI