F28335 SCIA sending only 2 bytes

Gergo Santha

Hi!

In have my SCI setup with RX interrupt, no TX interrupt and no FIFO. The RX part is fine, however I can't TX out more than 2 bytes. Here are my initial settings:

SciaRegs.SCICCR.all =0x0007; // 1 stop bit, No loopback
// No parity,8 char bits,
// async mode, idle-line protocol

SciaRegs.SCICTL1.all =0x0003; // enable TX, RX, internal SCICLK,

// Disable RX ERR, SLEEP, TXWAKE

SciaRegs.SCICTL2.bit.RXBKINTENA =1;

SciaRegs.SCIHBAUD =0x0001; // 9600 baud @LSPCLK = 37.5MHz.
SciaRegs.SCILBAUD =0x00E7;

SciaRegs.SCICTL1.all =0x0023; // Relinquish SCI from Reset

My TX out part:

SciaRegs.SCITXBUF=0x55;
SciaRegs.SCITXBUF=0x56;
SciaRegs.SCITXBUF=0x57;
SciaRegs.SCITXBUF=0x58;

The resulting output is:0x56 and 0x58. Watching the SCICTL2 register, I can see the following sequence:

-After writing 0x55 into TXBUF, TXRDY asserts

-After writing 0x56 into TXBUF, TXRDY de-asserts

-After writing 0x57 into TXBUF, SCICTL2 doesn't change

-After writing 0x58 into TXBUF, SCICTL2 doesn't change

Clearly, it is something important which I have overlook in the SCI datasheet. It would be great if someone would point my the right direction. Thank you.

over 15 years ago

0 Vamsi Gudivada over 15 years ago

TI__Guru* 87155 points

Greg,

TX buffer might be getting overwritten even before it gets transmitted out.

Use TXRDY/TXEMPTY to know the status of transmitter buffer register/transmitter shift register before writing to the TX buffer.

Thanks and regards,

Vamsi

0 Dean Hedin over 15 years ago

Prodigy 110 points

Make sure the previous character gets shifted out first, like this...

void scia_xmit(int a)
{
    // wait for previous char to go out.
    while (SciaRegs.SCIFFTX.bit.TXFFST != 0)
   {
    }
    SciaRegs.SCITXBUF=a; //stick it in...

}

0 Vamsi Gudivada over 15 years ago in reply to Dean Hedin

TI__Guru* 87155 points

Dean,

TXFFST is used when FIFO is used.

If FIFO is not used, TXRDY or TXEMPTY have to be used. Greg mentioned in his post that he is not using FIFO.

Regards,
Vamsi

0 Gergo Santha over 15 years ago in reply to Vamsi Gudivada

Genius 3585 points

Vamsi,

that was the problem, thanks for your reply. Now I changed my TX function:

SciaRegs.SCITXBUF=a;
while (!SciaRegs.SCICTL2.bit.TXEMPTY) {}

and now it works fine.

0 Dean Hedin over 15 years ago in reply to Gergo Santha

Prodigy 110 points

Sorry, my bad. But you know what? At the very least he should be using the TX FIFO!

Otherwise the foreground code will forever be waiting for slow serial characters to go out. 1 char @ 115200 baud is an eternity for these proccessors.

So as a next step, Greg, try enabling the TX FIFO, it's not that hard.

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F28335 SCIA sending only 2 bytes