Three keys on the keyboard at the same time

[Samoteph]

Hello everyone,

I am developing the game Miracle Boy In Dragon Land.
I am facing a problem with the game controls.
When I press two keys on the keyboard at the same time for example DOWN+RIGHT I can no longer press SPACE to hit. On the joystick it is the same problem but more restricted (only UP+LEFT+FIRE) which poses a problem.
I find the problem on games like RTYPE+ or Blood Money.
Is this a known problem on the hardware (Atari ST/Ste) or on the software side (ACIA manager)?

The only information I have on this subject is this post https://www.atari-forum.com/viewtopic.php?t=30715 which seems to be clear on the hardware part.

What do you think?

[mikro]

On the joystick it is the same problem but more restricted (only UP+LEFT+FIRE) which poses a problem.

This sounds suspicious. I don't see a reason why this combination shouldn't work. Every direction and fire button has its own line in the DSUB9 connector, there's no conflict.

[Greenious]

It's down to whatever keyboard handling routine you use I guess.

The keyboard itself has no such restrictions, it reports when a key is pressed, and when it is released. It is up to the keyboard handler to keep the tabs correct.

[AnthonyJ]

There was also some discussion in the Bad Mood thread about this issue (on Falcon, but I guess it's similar): https://www.atari-forum.com/viewtopic.p ... 51#p243251

[MasterOfGizmo]

The keyboard itself has these restrictions. Nearly any keyboard arranges the keys in a matrix which reduces the necessary connections required on the keyboard controller. It's physically possible to exactly identify two keys being pressed at once but a third key is.not exactly identifiable. Some keys occupy a complete row or column in the matrix "wasting" several key codes and reducing the number of keys installable. But these can be detected additionally. Keys like shift and control are usually implemented that way.

Do you really need to use the space key? If you can live with two cursor keys and e.g. shift then this might work.

[zerkman]

It's just how the IKBD (ST keyboard) processor is programmed. As already said, it can manage two simultaneous "ordinary" key presses plus the shifts, alt, control, caps lock which are managed separately.

[Greenious]

The keyboard itself has these restrictions.

Doh! I feel stupid, you are obviously correct. The matrix construction of the keyboard limits what keys can be detected at the same time.

If you look at the "Atari Mega ST Keyboard schematic" from the Atari Document Archive, you can see the layout of the keyboard matrix.

two keys are never a problem to identify, but more can be a problem, depending on how they share a row/column with the first two and, in what order they are pressed. (which is why ctrl, alt and the shift keys are on their own columns, more or less anyway, the last 3 shares it with f1-f3.) For example, If you press i and o, and the u (or p), in that order, u (or p) won't be detected, but if you press in the order of i, u and then o, it should detect all three correctly.

But as you can see on the matrix below, space have no row/column in common with the arrow keys and should be no problem.

kbd matrix.png

But it is also up to the keyboard handling routine. The IKBD reports when it detects a key being pressed, and when it is released. And if it reports more pressed keys, the keyboard handler must be able to handle that.

[Samoteph]

Thanks you all for your help with this problem

Here a link to the ACIA handkler I use for the game.

This is Daniel Hedberg's work that I modified for my needs:
https://1drv.ms/u/s!AvFd4WDBeDUns74UeYN ... A?e=5cfAOp

[Samoteph]

If I replace Space by Shift Left I can use two supplementary keys. So I guess the software part seems to be ok.