Problem processing "back-to-back" characters using SCI on MC9S08QE

Mr_Freez — Tue, 21 Jul 2009 00:39:43 GMT

I am having an issue recieving characters from a serial device. The device sends characters without any idle time in between bytes. For example, the device is supposed to respond with "OK<CR>" (3 byte response) upon receiving a specific command.

I only recieve the first character and overrun on the 2nd. I have tried polled mode and interrupts without any success. I have also cranked up the processor speed to 40MHz.

For interrupt mode, i initialize the peripheral as follows...

/* configure SCI2 interrupt mode */
/* SCI2C1: LOOPS=0,SCISWAI=0,Rsrc=0,M=0,WAKE=0,ILT=0,PE=0,PT=0 */
SCI2C1 = 0x00;               /* Configure the SCI */
/* SCI2C3: R8=0,T8=0,TXDIR=0,TXINV=0,ORIE=0,NEIE=0,FEIE=0,PEIE=0 */
SCI2C3 = 0x00;               /* Disable error interrupts */
/* SCI2S2: LBKDIF=0,RXEDGIF=0,??=0,RXINV=0,RWUID=0,BRK13=0,LBKDE=0,RAF=0 */
SCI2S2 = 0x00;
/* SCI2C2: TIE=0,TCIE=0,RIE=0,ILIE=0,TE=0,RE=0,RWU=0,SBK=0 */
SCI2C2 = 0x00;               /* Disable all interrupts */
SCI2BD = UART_BAUD_9600;

      /* SCI2C3: ORIE=0,NEIE=0,FEIE=0,PEIE=0 */
SCI2C3 |= 0x00;                      /* disable error interrupts */
SCI2C2 |= ( SCI2C2_TE_MASK | SCI2C2_RE_MASK | SCI2C2_RIE_MASK); /* Enable transmitter, Enable receiver, Enable receiver interrupt */
asm CLI;

My isr looks like...

void vSci2Rx(void){
char cDummy;
//clear the isr source
cDummy = SCI2S1;//dummy read to clear
//read the char into buf
ucRcvBuf[i++] = SCI2D;
//check for overrun
if(SCI2S1_OR){
cDummy = SCI2D;
}
}

Any ideas on how to improve thru-put w/ this peripheral?

regards

rich

Re: Problem processing "back-to-back" characters using SCI on MC9S08QE

bigmac — Tue, 21 Jul 2009 02:47:02 GMT

Hello Rich,

This thread is actually posted in the wrong forum, since your query concerns an 8-bit device.

For a data rate of 9600 baud, you have more than 1ms between characters, and this delay is needed for an overrun to occur. Your SCI receive ISR execution would appear to be considerably shorter than this.

Is it possible that you have other more lengthy ISRs that may delay the processing of the SCI receive?

Regards,

Mac

Re: Problem processing "back-to-back" characters using SCI on MC9S08QE

Mr_Freez — Tue, 21 Jul 2009 04:45:35 GMT

Sorry, my bad...will repost this on the 8 bit forum...thx

8-bit MicrocontrollersのトピックRe: Problem processing "back-to-back" characters using SCI on MC9S08QE

Problem processing "back-to-back" characters using SCI on MC9S08QE

Re: Problem processing "back-to-back" characters using SCI on MC9S08QE

Re: Problem processing "back-to-back" characters using SCI on MC9S08QE