Connecting 24 Bit SPI Slave to TM4C12336H6PZ

Hi,

I presume you will use Moto/Freescale mode - and in this case, back to back transmission will work with all modes, except mode 0. This means you can/must send two 12bit words without SSIFss going inactive (high). And of coarse, your solution to use a GPIO pin for SSIFss will also work. ( in Moto mode 0 SSIFss going high transfer the data to internal registers...).

Petrei

Hello Petrei,

are there any configuration settings avoiding SSIFss going inactive between two SPI cycles? In datasheet I couldn't find any. Thus the workaround with GPIO.

Thomas 

Hi,

This mode is managed by the module's FIFO - as long as you have a word in FIFO, it is sent; when the last bit is transmitted and no more words, the SSIFss is rised up so you must wait tor the transmission duration before sending another words.

You can try both solutions and see which one is better for you.

Petrei

Hello,

in TM4C1233H6PZ datasheet refers to two SPI modes single mode and continous mode - in continous mode SSIFss going high between the SPI cycles. I pictured to myself continous mode is effected by using the FIFO's. So my question in particular is: "How can a set SPI in continous mode or in the mode SSIFss not going high between two cycles?"

Thomas 

Hi,

I already told you about in my previous answer, but take care about modes:mode 0 is the single one which rises SSIFss for every transmitted word, single or continuous. In all others: single=one word then wait until the last bit is transmitted, then send others same way; continuous=fill the FIFO then wait until empty.

Petrei

Hi,

I had responded on a similar thread for 40-bit. You can use SPO=0 and SPH=1 with DSS=8. But you have to make sure that the FIFO is written with the 3 bytes so that they can transmitted in continous mode and the CS remain low for the 24 bits.

Amit

@Amit,

Seems you have a single, universal recipe for all cases. Please take into account that most, but not all devices to be used with SPI have implemented only mode 0 and 3. 

Petrei

@Petrei

Yes, that is true about most devices supporting Mode0 and Mode3 and the recipe on TM4C123 as the solution. On TM4C129 one can use MODE-0 with Frame Hold Feature to make 8xn bits worth of transfer.

Amit

So, in this case, we won't be able to use Tivaware directly..? 

Any example code on how to do the initialization and writing into it ?

Thank you

Hi,

Depends - you can use Tiva function directly or write something like this:

SSIDataSend24(uint32_t ui32Base, uint32_t ui32Data)
{
  //
  // Check the argument... do it yourself
  // 
  
  //
  // Wait until there is space
  // 
  while(!(HWREG(ui32Base + SSI_O_SR) & SSI_SR_TNF))
    {
    }

    //
    // Write the data to the SSI.
    //
    HWREG(ui32Base + SSI_O_DR) = (ui32Data & 0x00FFF000)>>12;
    HWREG(ui32Base + SSI_O_DR) = (ui32Data & 0x00000FFF);
    SysCtlDelay(650); // allow delay to permit transmission and SSIFSS to rise up
}

You must adjust the delay to be equal to transmission time + minimum SSIFSS time (50ns).

If you need to receive also, must add the receiving part.

Petrei 

Hi Petrei,

Any example code on how  to do it using tivaware ?

Thank you

// set GPIO pin LOW - do it by yourself
SSIDataPut(mySSI, (myData & 0x00FF0000)>>16);
SSIDataPut(mySSI, (myData & 0x0000FF00)>>8;
SSIDataPut(mySSI, myData & 0x000000FF;
// set here GPIO pin HIGH - do it by yourself

Hi,

The above example is not with Tiva written?

OK, something different - with a GPIO pin as SSIFSS:

ok, Thanks Petrei

Hi there,

As it was suggested I tried to send my frame in 3 bytes and this seems to work fine with SSI_FRF_MOTO_MODE_1. However when I use SSI_FRF_NMW it seems that before each of the 3 bytes a zero byte is send. Does anyone know if this transmission is feasible with SSI_FRF_NMW (MicroWire)?

Thanks,

Kimon