e.g. in a texteditor these are used for selecting text.

The keyboard generates an interrupt, so the keystroke can be detected
with keypressed, but the value returned by readkey is the same as for the
keys without the shift.
The same for the FAQ 78 solution for detecting F11 and F12. (BTW. This
procedure lacks a keypressed check)

Of course it is possible to poll the keyboard and look for one of the
shift keys. (see the example program below). But the danger is that the
shift state is missed by the poll if there is a time consuming procedure
in the loop. OTH  I noticed that upon de-pressing the arrow, pgup/dn
home/end key, a shift down key scan is generated again if shift remains
down.

--
Femme

PS The code for checking the keyscan is.

Greetings

hello. i hope this table will help you:

segment $0040

 17h    BYTE    Keyboard status flags 1:
                    bit 7 =1 INSert active
                    bit 6 =1 Caps Lock active
                    bit 5 =1 Num Lock active
                    bit 4 =1 Scroll Lock active
                    bit 3 =1 either Alt pressed
                    bit 2 =1 either Ctrl pressed
                    bit 1 =1 Left Shift pressed
                    bit 0 =1 Right Shift pressed
 18h    BYTE    Keyboard status flags 2:
                    bit 7 =1 INSert pressed
                    bit 6 =1 Caps Lock pressed
                    bit 5 =1 Num Lock pressed
                    bit 4 =1 Scroll Lock pressed
                    bit 3 =1 Pause state active
                    bit 2 =1 Sys Req pressed
                    bit 1 =1 Left Alt pressed
                    bit 0 =1 Left Ctrl pressed

i've tested this before posting, it worked for me.

you can read the keyboard status flags using mem[$0040:$0017] and
mem[$0040:$0018] in tp6+. then you will have to check for what values
do you need.
example. you need to check if left shift is pressed

var a : byte;

(* check point *)
a := mem [$0040:$0017];

if (a and $02) <> 0 then begin
(* left shift is pressed *)
end;

this is a simple example, maybe not that syntax right for pascal, but
easy to understand.

greetings
Vasko

I made a few changes  in order to make it work for protected mode. (while
keeping backward compatibility)

{$ifndef ver70}
const seg0040=$0040;
{$endif}
.....
      if (mem[seg0040:$0017] and $3)<>0 then write(' shift');
      if (mem[seg0040:$0017] and $4)<>0 then write(' ctrl');
      if (mem[seg0040:$0017] and $8)<>0 then write(' alt');