SPI Character Length and FIFO Question F28075

Lance,

You will want to use 3 writes to the SPITXBUF. You will left-shift the 8-bit word to be transmitted in each write. Essentially, the first 16-bit word will be transferred to the shift register where the upper 8 bits will be shifted out to the data line.then the SPI will copy the next 16-bit word in the FIFO to the shift register and repeat. The F2807x SPI has a 16-level FIFO regardless of the word size. For example, you can store sixteen 2-bit words, or you can store sixteen 16-bit words in the FIFO without any data packing.

Thanks,
Mark

Mark,

I think I understand what you are saying.  Here is a quick bit of code I put together which I believe should work (may need refinement) as I want based on your advice.

I configure the SPI peripheral for 8 bit characters and FIFO operation.  I also include code to parse the 16 bit data to send it out in separate chunks left justified.  I execute 3 sequential writes to the SPITXBUF register to start filling up the FIFO. Based on my understanding from your explanation this would end up creating the continuous 24-bit long data stream on the SPISIMOA pin.  Is that correct?

Somewhere else in code I would plan to use the interrupt flag to tell when the SPI module has finished sending out the data, but omitted it. 

void SPI_DAC_CNF(){
//SPI Register Configuration
    //SPICCR Registers
    SpiaRegs.SPICCR.bit.SPISWRESET = 0;
    SpiaRegs.SPICCR.bit.SPICHAR = 0x7;  //8-bit characters
    SpiaRegs.SPICCR.bit.CLKPOLARITY = 0;  //Clock polarity (data out on rising clock edge)
    
    //SPICTL Reigsters
    SpiaRegs.SPICTL.bit.MASTER_SLAVE = 1;    //Configure as a master to transmit on SPISIMOA
    SpiaRegs.SPICTL.bit.CLK_PHASE = 1;    //Clock phase, half cycle offset
    SpiaRegs.SPICTL.bit.TALK = 1;    //Enable data transmit via SPI
    SpiaRegs.SPICTL.bit.SPIINTENA = 1;     //Enable SPI interrupts
    
    //SPIPRI Registers
    SpiaRegs.SPIPRI.bit.STEINV = 0;        //SPISTE bar acitve low
    SpiaRegs.SPIPRI.bit.TRIWIRE = 0;    //Normal 4 wire operation
    
    //SPIBRR Registers
    SpiaRegs.SPIBRR.all = 0;    //Set Baud rate to max rate, 15Mbaud
    
    //SPI FIFO Registers
    SpiaRegs.SPIFFTX.all = 0xC020;    //Set TX FIFO to throw a flag when the TX FIFO is empty
    SpiaRegs.SPIFFRX.all = 0x0023;    //Set RX FIFO to throw a flag when the RX FIFO has 3 entries
    SpiaRegs.SPIFFCT.all = 0x00;
    
    SpiaRegs.SPICCR.bit.SPISWRESET = 1;        //Enable SPI
    SpiaRegs.SPIFFTX.bit.TXFIFO=1;
    SpiaRegs.SPIFFRX.bit.RXFIFORESET=1;
}

void SPI_DAC_WRITE(unsigned int data)
{
    unsigned int address; //address variable, just a dummy varaible for this example.
    
    address = address << 8;  //left shift to make tx buff happy.
    
    //Conditioning on input data to be ready for 8 bit TX FIFO
    unsigned int arraydata[2];
    arraydata[0] = data << 8;
    arraydata[1] = data >> 8;
    arraydata[1] = arraydata[1] << 8;
    
    //Load up the TX buffer and FIFO with the 3 8-bit chunks to have SPI peripheral clock out the 24-bit string
    SpiaRegs.SPITXBUF = address;        //8 bit DAC address
    SpiaRegs.SPITXBUF = arraydata[1];    //8 MSBs of data
    SpiaRegs.SPITXBUF = arraydata[0];    //8 LSBs of data
}