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From: csd35@seq1.keele.ac.uk (Jonathan Knight)
Newsgroups: comp.os.msdos.programmer
Subject: Getting data from asynchronous serial ports
Message-ID: <768@keele.keele.ac.uk>
Date: 20 Dec 90 10:37:23 GMT
Organization: University of Keele, England
Lines: 44

Hi,

  I'm having trouble reading data from a serial port if the data arrives
at the maximum chars per second the baud rate allows.  If the data arrives
interspaced with pauses then it arrives perfectly.

Here is a short piece of code I've been using

main()
{	int i;

	for (i=0; i<100; ++i)
		printf("%d\t", inp(0x338));
}

The idea is to repeatedly read the port and just see what turns up.  I have
more complicated code that runs under interrupt and tests all sorts of bits
of the status register and things, but this was enough to see what was
happening.

If I connect a terminal to the port and type <esc>[A  (the codes the up
arrow generates) then I get to see 27 91 65 (lots of times for each).  If
I hit the up arrow key I get 27 171 255.

Now if I program a soft key with the same sequence I can adjust the rate that
the data is sent to the computer.  If I run at a baud rate of 4800 and set
the function keys to generate at 150cps then all goes fine.  If I let them
run at 480cps (max rate) then the 27 171 255 is seen again.  Note I get the
same sequence whatever baud rate I run at (even 300), but it always works
perfectly if I deliberately set the cps to less than max for the baud rate.

If anyone can shed any light then I'd be grateful.

-------------

I have lost the book I was using which dealt with the serial I/O stuff.
If anyone can type in a quick summery of the UART's ports then I'd
be forever grateful.  If anyone can summerise the PIC's commands, that
would help too.
-- 
  ______    JANET :jonathan@uk.ac.keele.cs     Jonathan Knight,
    /       BITNET:jonathan%cs.kl.ac.uk@ukacrl Department of Computer Science
   / _   __ other :jonathan@cs.keele.ac.uk     University of Keele, Keele,
(_/ (_) / / UUCP  :...!ukc!kl-cs!jonathan      Staffordshire.  ST5 5BG.  U.K.