Quick PC Assembly langue question

[Jack_www]

I am not sure if anyone here knows PC Assembly, but I have a project due tomorrow for my Assembly langue class. I just need to know how do I find out if some pressed up or down arrow keys on the keyboard. I am able to detect the key being pressed but I dont know what key is being pressed when it is not a character. Can anyone help me with this?

[trev]

All keys have an unique ASCII code number I think, just need to look up in textbook or manual what the code is for the key you are checking, should be a number in binary between 0 and 255.

[Jack_www]

I ran the program in debug. The value I got was zero for both up and down keys. I have an ASCII table of values and it did not work when I use it in the program

[Dr. A. Cula]

I ran into the same problem years ago, but I was using C. IIRC, the solution was to test the keyboard again when I got a 0.

[Zoid]

I´ve done my fair share of PC Assembly, all you need is a screwdriver really...

[Jack_www]

Originally posted by Dr. A. Cula
I ran into the same problem years ago, but I was using C. IIRC, the solution was to test the keyboard again when I got a 0.

I tested it a number of times, and I still get zero. The program responds when I press the up and down arrows, just that the value is always zero.

[Jack_www]

Right now since I cant figure this out, I am using the w key for up and the s key for down.

[VetLegion]

Maybe you are checking the wrong register? You need to post some code. For example:

mov ax, 0       ; parameter 1
mov bx, 2       ; parameter 2
int 21h            ; interrupt
mov dx, ax     ; put result into dx

...and add comments to what does what. I've done some assebbler stuff before, maybe I can recall something and help you out.

[Jack_www]

Here is a short sample of the code I am using:

mov ah,01h  ;using 1h so that the program does not wait for key to be pressed, it is only checking to see if it is
int 16h ;do the interrupt
	
jz mainloop ;Zero flag is set if no key is pressed

;go on to check what key was pressed and process input

[Dr. A. Cula]

I found some (rather sketchy) doc that seems to confirm that int 0x16, function 0x01 returns 0 in AL for function keys (http://www.htl-steyr.ac.at/~morg/pci...s/inte1at0.htm).

But it also says that AH contains that key's scan code and I think you should use that if AL is 0. Here is a list of keyboard scan codes: http://www.cs.cmu.edu/afs/cs/user/ra...WWW/files.html (I found it in the part A archive, in the INTERRUP.A file). Also see the INTERRUP.D file for some more info on int 0x16.

[Jack_www]

Originally posted by Dr. A. Cula
I found some (rather sketchy) doc that seems to confirm that int 0x16, function 0x01 returns 0 in AL for function keys (http://www.htl-steyr.ac.at/~morg/pci...s/inte1at0.htm).

But it also says that AH contains that key's scan code and I think you should use that if AL is 0. Here is a list of keyboard scan codes: http://www.cs.cmu.edu/afs/cs/user/ra...WWW/files.html (I found it in the part A archive, in the INTERRUP.A file). Also see the INTERRUP.D file for some more info on int 0x16.

I will try that, thanks.

[Provost Harrison]

I used to do assembler on BBC microcomputers many a year ago. However I doubt this is going to help you much, however

[snoopy369]

I'm quite sure you need to check a second value for function keys like the arrow keys. I don't know assembly at all, but I know that in BASIC and other languages that pick up ASCII for arrow keys, you get a 0 and then another value for keyboards (appears visually with a ^, like ^M for enter).

[Jack_www]

I ran it in debug and the value was stored in AH, thanks Dr. A. Cula that was a real big help.

[Jack_www]

I just put it into my program and it works perfect.