Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!osu-20.ircc.ohio-state.edu!laufman-h
From: LAUFMAN-H@osu-20.ircc.ohio-state.edu (Harry Laufman)
Newsgroups: comp.lang.pascal
Subject: Readkey without "use crt" (Was Re: Strobing the keyboard)
Keywords: keyboard, read, keypressed
Message-ID: <12544333713034@osu-20.ircc.ohio-state.edu>
Date: 22 Nov 89 20:03:08 GMT
Sender: news@tut.cis.ohio-state.edu
Organization: The Ohio State University, Columbus, Ohio
Lines: 63

KeyBoard reading without Unit CRT.
I have used FUNCTION KEYHIT instead of KEYPRESSED for quite awhile
now since it is demonstrably faster.  On reading the "Readkey without
Unit CRT" query, it seemed it could be done by reading memory directly
with the Turbo Mem and MemW (byte and word based) arrays.  With the
help of the cited manual I pieced together a Turbo 5.5 compiled code
which seems to work OK.  I did find I had to re-assign the keyboard
buffer head address to the keyboard buffer tail address.  Apparently
the Turbo call to ReadKey does this.
Good Luck, Harry LAUFMAN-H@osu-20.ircc.ohio-state.edu
Reference and source code follow:
--------------------------------------------------------------------------
                        DOS TECHNICAL INFORMATION
 Programming Technical Reference - IBM
 Copyright 1988, Dave Williams  { found a DOSTECH.ZIP on many BBSs }
 { many lines omitted }
                   Reserved Memory Locations in the IBM PC
 
addr.  size            description
 { many lines omitted }
40:17  byte    keyboard flag byte 0 (see int 9h)
               bit 7  insert mode on      3  alt pressed
                   6  capslock on         2  ctrl pressed
                   5  numlock on          1  left shift pressed
                   4  scrollock on        0  right shift pressed
40:18  byte    keyboard flag byte 1 (see int 9h)
               bit 7  insert pressed      3  ctrl-numlock (pause) toggled
                   6  capslock pressed    2  PCjr keyboard click active
                   5  numlock pressed     1  PCjr ctrl-alt-capslock held
                   4  scrollock pressed   0
40:19  byte    storage for alternate keypad entry (not normally used)
40:1A  word    pointer to keyboard buffer head character
40:1C  word    pointer to keyboard buffer tail character
40:1E  32bytes 16 2-byte entries for keyboard circular buffer, read by int 16h
{ many lines omitted }
-----------------------------------------------------------------------------
program readmem;
{** This could certainly be tersed up with lose of clarity **}
var
    Address : Word;
    AChar   : Char;
 
Function KeyHit:Boolean;
begin KeyHit := Mem[$0040:$001A] <> Mem[$0040:$001C] end;
                { Kbd Buffer Head <> Kbd Buffer Tail }
begin
Writeln('*** Begin ***');
Achar := 'a';
 
Repeat
If Keyhit then
   begin
   Address := MemW[$0040:$001A];        { Where the Kbd Buffer Head is }
   AChar   := Chr(MemW[$0040:Address]); { What it is }
   Mem[$0040:$001A] := Mem[$0040:$001C];{ Set Head = Tail }
   writeln(AChar);                      { See what we got }
   end;
Until AChar = 'x';                      { A way out }
 
 
Writeln('*** End ***');
readln;                                 { Wait for <Enter> }
end.