Scan Codes 3

[spec85]

Hi

I'm new to assembly so do forgive me if I have overlooked something.

I am writing a program that waits for the ctrl + alt + a keys to be pressed at the same time.
I’m using int 16h function 00h to get the key and cmp that it is a ‘a’

I then want to use int 16h function 2h to see if the ctrl + alt keys where pressed.

These two functions work fine separately but when put together they don’t work.
The problem is when you are holding ctrl + alt, ‘a’ doesn’t = ‘a’ anymore.

How can I get around this? Should I be using the a scan code?
If so what is the scan code for ctrl + alt + a?

Thanks for any help you can offer

Spec

 

[OSProgrammer]

Hello!

Here Is INT 16 Scan Codes =>

http://www.iro.umontreal.ca/~feeley/cours/ift2240/doc/assembly/scancodes.html

Use These Scan Codes INT 16,00.

Best Regards...
OSProgrammer

 

[spec85]

The Below program is ment to: loops waiting for a letter. Then checks the scan code equals "1E01" which should be ctrl+A.

http://www.iro.umontreal.ca/~feeley/cours/ift2240/doc/assembly/scancodes.html

Sadly it doesn't work. What am I doing wrong?

START:
mov ax, @DATA
mov ds, ax

letterLoop:
mov ah, 00H
int 16h ;get a key, return in AX

mov al, ah ;copy scan code into al
cbw ;move ah into ax
cmp ax, 1E01H
jne letterLoop

mov ax,4c00h
int 21h ;end program


END START

 

[lionelhill]

have a look at what cbw does. All it does is extend the sign-bit (highest bit) of a byte to fill the whole word, thus preserving negative-value bytes as negative-value words. After cbw, the top half of ax (which is exactly the same thing as saying ah) will always be 0 or 0FFh. It can't ever be 01Eh

 

[spec85]

OK
what if I
int 16,00
cmp al,'a'
if yes
then
int 16,02
cmp al, 00001100B

Shouldn't that work?

 

[adholioshake]

Why don't you try using the 'Get Keyb. Flags' BIOS function (ah=02h, int 16h). The return byte in AL gives keyboard flags...

AL: bit description
00h r. shift
01h l. shift
02h CTRL
03h ALT
04h SCROLL LK
05h NUM LK
06h CAPS LK
07h INSERT

As an example of what I mean, look at the following code:

key_loop:
  mov ah,02h
  int 16h
  and al,0ch
  cmp al,0ch
  jne key_loop
  mov ah,00h
  int 16h
  cmp al,'a'
  je key_press
  cmp al,'A'
  je key_press
  jmp key_loop

key_press:

The code is slightly flawed in that the keyboard buffer is not emptied before cmp to 'a' or 'A'. I'll leave you to do some of the work...


Don't hate the player - hate the game

 

[spec85]

Thanks for all your help. I finally got it working.
I actually read port 60h testing for the scan code of 'a'
then I did int 16, 02 to test for ctrl+alt

Thanks!