From: deleveld AT my-deja DOT com
Newsgroups: comp.os.msdos.djgpp
Subject: Source for bioscom at 19.2k and some questions
Date: Mon, 05 Jul 1999 14:25:26 GMT
Organization: Deja.com - Share what you know. Learn what you don't.
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hello Everyone,

I've been working on some serial communication stuff and
I found that bioscom commands only work up to 9600 baud, and
I wanted to use them at 19.2 kbaud.  There is some source
to do this at the end of this post.

What I need to find out now, is how to read from the port
_without_ hardware handshaking.  It seems bioscom just calls
INT 14, and that seems to require hardware handshaking.  The
reason that I cannot use handshaking is that the device that
I must communicate gets its power from RTS and DTR and they
need to be high and low for the interface to work.

I guess I also need to find out how I can arbitrairly assert
RTS and DTR without affecting the serial comm.

So if anyone knows these things, please post or mail me.

Thanks,

Doug Eleveld

/* Figure out the Port address for a given COM port */
static unsigned short COMPort(const t_comport com)
{
  switch(com)
  {
    case(COM1):
      return 0x03F8;
    case(COM2):
      return 0x02F8;
    case(COM3):
      return 0x03E8;
    case(COM4):
      return 0x02E8;
    default:
      perror("Illegal com port in function COMPort");
      exit(1);
  }
}


static void forcebaud(const t_comport com, const int baud)
{
  int ints_were_enabled;

  int divisor;
  unsigned char divlow, divhigh;

  unsigned short Port = COMPort(com);

  unsigned short LCR  = 3 + Port;  /* The address of the line Control
Register */
  unsigned short BRDH = 1 + Port;
  unsigned short BRDL = Port;

  unsigned char LCRContents;

  /* Make sure we have a reasonable baud rate */
  if(!baud)
    return;

  /* Figure out the baud rate divisor */
  divisor = 115200 / baud;
  divlow = divisor & 0xff;
  divhigh = (divisor >> 8) & 0xff;

  /* Get the old data from the LCR port */
  ints_were_enabled = disable();
  LCRContents = inportb(LCR);

  /* Mask on bit 7 for DLAB registers */
  outportb(LCR, LCRContents | 0x80);

  /* Set Baud Rate divisor */
  outportb(BRDL, divlow);
  outportb(BRDH, divhigh);

  /* Put the old data back */
  outportb(LCR, LCRContents & 0x7f);

  if(ints_were_enabled)
    enable();
}


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