CCS/TM4C1294KCPDT: How to use SSI as SPI having muxed CS line instead of direct GPIO pin?

scenario briefing:

I have used pinmux tool to configure pins for SSI1 port. only using the configurations for SSI1XDAT0, SSI1XDat1 and SSI1CLK and for Chip select
i aim external handling of muxed CS line, selecting the chip while writing() the again disabling it after performing operation similar for reading(). but unable to read the ADC LTC1863 values.

please correct me where ever required. and guide me for correct approach.

Thanks

Anan,

Using a GPIO for CSB is actually much more recommended than letting the standard hardware take care of it (because it will likely control it in a non-compatible timing, for SPI is "too flexible"...)

This is a piece of code that is proven to work for one particular type of sensor. Maybe it will help you . It does use a GPIO for CSB, and reads a small sequence of bytes. I'm not including the configuration part, as you seem to be on the way there.

    GPIOPinWrite(gyroHW->GPIOFSSPort,gyroHW->GPIOFSSPin,0);       // Lower CSB
    SSIDataPut(gyroHW->SSIBase, frameHigh);                       // Sends only the upper 16 bits
    while(SSIBusy(gyroHW->SSIBase));
    SSIDataGet(gyroHW->SSIBase, &readCrap);                       // Read useless data
    SSIDataPut(gyroHW->SSIBase, (frameLow));                      // This sends the other 16 bits
    while(SSIBusy(gyroHW->SSIBase));
    GPIOPinWrite(gyroHW->GPIOFSSPort,gyroHW->GPIOFSSPin,gyroHW->GPIOFSSPin);     // Raise CSB
    SSIDataGet(gyroHW->SSIBase, &readCrap);                       // Read useless data
    GPIOPinWrite(gyroHW->GPIOFSSPort,gyroHW->GPIOFSSPin,0);       // Lower CSB
    SSIDataPut(gyroHW->SSIBase, frameHigh);                       // Flush 16 more bits
    while(SSIBusy(gyroHW->SSIBase));                              // Wait for bits to be flushed out
    SSIDataGet(gyroHW->SSIBase, &read16High);                     // Read 16 bits
    SSIDataPut(gyroHW->SSIBase, frameLow);                        // Flush 16 more bits
    while(SSIBusy(gyroHW->SSIBase));                              // Wait for bits to be flushed out
    SSIDataGet(gyroHW->SSIBase, &read16Low);                      // Read more data
    GPIOPinWrite(gyroHW->GPIOFSSPort,gyroHW->GPIOFSSPin,gyroHW->GPIOFSSPin);     // Raise CSB

Regards

Bruno

Hi Bruno,

Thanks a lot for your reply. But I have figured out the issue in my case. It was in SSIConfigSetExpClk() configuration. I could have checked it before. so, yeah its my bad... :P 

But anyways, Now i can work with Multiplexed Chip select line and can save other GPIOS for other purpose. 

problem was here:

SSIConfigSetExpClk(SSI1_BASE, ui32SysClock, SSI_MODE_MASTER,SSI_MODE_MASTER, 1000000, 8);

And the corrected configuration:

SSIConfigSetExpClk(SSI1_BASE, ui32SysClock, SSI_FRF_MOTO_MODE_0,SSI_MODE_MASTER, 1000000, 8);

 

I can read ADC ltc1863 data, and yes this is still under test so cant say much abut its behaviour, But over all project is is stable till now.

Thanks once again Bruno.

Regards

Anan