Serial Programming - upload.wikimedia....

Serial DOS
the Escape key will be used to quit the program, which will in fact be where most of
the changes to the program will happen. We are also introducing for the first time
direct output into the UART instead of going through the standard I/O libraries with this line:
Port[ComPort[1] + THR] := Ord(OutputLetter);
The Transmit Holding Register (THR) is how data you want to transmit gets into
the UART in the first place. DOS just took care of the details earlier, so now we
don't need to open a "file" in order to send data. We are going to assume, to keep
things very simple, that you can't type at 9600 baud, or roughly 11,000 words per
minute. Only if you are dealing with very slow baud rates like 110 baud is that going
to be an issue anyway (still at over 130 words per minute of typing... a very fast typist indeed).
program SimpleTerminal;
uses
Crt;
const
THR = 0;
RBR = 0;
LCR = 3;
LSR = 5;
Latch_Low = $00;
Latch_High = $01;
{Character Constants}
NullLetter = #0;
EscapeKey = #27;
var
ComPort: array [1..4] of Word absolute $0040:$0000;
InputLetter: Char;
OutputLetter: Char;
begin
Writeln('Simple Serial Data Terminal Program. Press "Esc" to
quit.');
{Change UART Settings}
Port[ComPort[1] + LCR] := $80;
Port[ComPort[1] + Latch_High] := $00;
Port[ComPort[1] + Latch_Low] := $0C;
Port[ComPort[1] + LCR] := $03;
{Scan for serial data}
OutputLetter := NullLetter;
repeat
if (Port[ComPort[1] + LSR] and $01) > 0 then begin
InputLetter := Chr(Port[ComPort[1] + RBR]);
Write(InputLetter);
end; {if}
if KeyPressed then begin
OutputLetter := ReadKey;
Port[ComPort[1] + THR] := Ord(OutputLetter);
end; {if}
until OutputLetter = EscapeKey;
end.
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