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Marcel Vander Mierde
Delphi Developer |
Wed, 18 Jun 1902 08:00:00 GMT
Reading function/cursor keys
"Osmo Ronkanen" <ronka...@cc.helsinki.fi> schreef in bericht
news:8i0uu8$j96$1@kruuna.Helsinki.FI...
Quote> In article <NTR05.171440$Qp2.442...@afrodite.telenet-ops.be>,
> Marcel Vander Mierde <Marcel.Vander.Mie...@pandora.nospam.be>
wrote:
> >This is my point of view - so if I'm wrong, please correct me.
> >Apparently, every key or keycombination fills the keyboardbuffer
with
> >two bytes (a word?), probably to fill up the 16 bits. When pressing
a
> >special key or keycombination the second byte will get the
(hex)value
> >00. This is what I can deduct from reading all those 'special key'
> >codes.
> >If the compiler reads the buffer he will first read the second
byte.
> >when a 00 is met, he 'knows' another byte is{*word*154} around and
will
> >not clear the buffer until asked to do so,
> >however when the second byte does not equal 00, a 'normal' key is
> >pressed and the buffer will be cleared automatically (?).
> >As I stated before, this is my humble opinion, so if anyone knows
more
> >about this:
> >I'm always willing to learn.
> >Hope this helped a Bit,
> I do not know what you are talking about. The internal
representation
> of the keyboard buffer is not relevant. What Readkey does is it uses
Int
> 16h, ah=0 to read a scancode, ASCII code pair. It returns the ASCII
> code. If the ASCII code is zero, then it stores the scan code into
an
> internal buffer. The next time it is called it checks the buffer if
> there is scancode available and if there is it is returned instead.
> Here are Pascal versions of readkey and keypressed:
> const scancode:char=#0;
> function readkey:char;
> var rg:registers;
> begin
> if scancode>#0 then begin
> readkey:=scancode;
> scancode:=#0;
> exit;
> End;
> rg.ah:=0;
> intr($16,rg);
> readkey:=chr(rg.al);
> if rg.al=0 then scancode:=chr(rg.ah);
> End;
> function keypressed:boolean;
> var rg:registers;
> begin
> if scancode>#0 then keypressed:=true
> else begin
> rg.ah:=1;
> intr($16,rg);
> keypressed:=rg.flags and fzero=0;
> End;
> End;
> Note that the buffer where the scancode is store is internal to CRT,
it
> has nothing to do with the BIOS keyboard buffer.
> Osmo
thanks for clarifying things up for me,
I saved your answer to my harddisk (as I do with many others), so I
can learn from it.
As I said in my posting, my "guess" was a deduction from the things I
knew and saw.
Still, I'm stuck with the same question as Frederic, what is the
meaning of this high byte for a "normal" key, or isn't there a meaning
at all?
Marcel
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