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CCS/TM4C123GH6PM: Initialization SSI unit with two CS lines

Ali Naseri
Prodigy 180 points

Part Number: TM4C123GH6PM

Tool/software: Code Composer Studio

Hi,

I want to use the SSI unit of the TIVA C microcontroller to control a small 3.5" TFT.

That TFT is controlled by SPI and has also a touch screen controller with a secound SPI interface.

So  I want to attach both SPI peripherals on the same SSI unit, but the initialization routine of the SSI unit has also one chip select line.

But I need two independent chip select lines. Is there a possibility to initialize the SSI unit without dedicated chip select line or assign two chip select lines to the unit??

  • 0
    TI__Guru 72500 points
    There is only one SSInFss (Frame sync signal), which is often used as SPI chip select, per SSI module. You have two options. First, you can use two arbitrary GPIO pins as outputs attached to the two TFT chip select inputs. By software drive the proper one active (usually low) when you want to read or write to that interface, then drive it back high before you switch to the next interface.

    If you need the chip select signal to toggle at the end of each transmission, you may want to use the read FSS signal instead. SSI1Fss is available on two different port pins, PD1 and PF3. You can change the configuration such that one pin is SSI1Fss and the other a GPIO output in the "inactive" state. Then switch the configuration when you want to talk to the other SPI slave.