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I can't get familiar with PUTCHAR and PUTS

Michal Selinger

I've got a problem. I've posted it yesterday but it was probably lost in text.

static void Nastav_seriovy_kanal (void)
{
	SCON = 0x50;
	TMOD = TMOD | 0x20;
	TH1 = 0xF4;
	TL1 = 0xF4;
	ES = 1;
	TR1 = 1;
}

static void Preruseni_seriovy_kanal (void) interrupt 4
{
	if (RI == 1)
	{
	    RI = 0;
	    if(SBUF == 'A') putchar('Q');
	}
	if (TI == 1) TI = 0;
}
I'm also including stdio.h, and string.h(string.h is not necessary).

Does anyone have any idea why it doesn't work?

Parents Reply Children
  • 0 in reply to Michal Selinger

    "I want to use PUTCHAR and later PUTS procedures to communicate through serial port."

    It is a very bad idea to try to use these in an interrupt service routine!

    For interrupt-driven serial IO, see:

    http://www.keil.com/download/docs/71.asp

    This shows you how to write a custom putchar to use interrupt-driven serial comms.

  • 0 in reply to Andy Neil

    It is a very bad idea to try to use these in an interrupt service routine!

    Well ... yeah.

    You can use them in an ISR, as long as you're aware that they are going to hog CPU cycles like crazy (they spinlock if the serial transmitter is busy) and that they're not reentrant.

    Also, I think there's some code putchar.c that could drop characters or enter an endless loop under certain rare circumstances. Something along the lines of

    do
{
  RI = 0;
  while(!RI);
} while(SBUF != XON)

    With some bad luck, RI goes to 1 at the beginning if the do loop, gets overwritten by a 0, and the while loop will run until the next character has been received.

    Certainly, the chances for this are minimal, but I don't see anything that would prevent the behavior.