Keyboard hardware questions
D. Peschel
Hello,
I'm new to this newsgroup (though I have plenty of experience with USENET
and computers). I grew up with the Apple ][ but I'm now playing with a few
Atari emulators. It's really interesting to compare the designs of 80's
machines (Apple, Atari, Commodore, Acorn) to see how they all resolved the
same design issues.
I've read the Atari System Manual and quickly looked at a couple of users'
guides, and the source to a couple of emulators. I'd like to really under-
stand what's possible and impossible with the keyboard hardware.
Would someone mind correcting me if I'm wrong?
- There are a few different physical arrangements of keys:
400/800, 1200XL, 600XL/800XL, XE's.
- Theoretically, a keyboard can be viewed as a matrix of
independent switches, so there are 2^n possible states
where n is the number of keys. But no 8-bit Atari provides
software or firmware access to this representation.
- Instead, there are a couple of different kinds of keystrokes:
The RESET and BREAK keys generate immediate interrupts.
(Is it possible to distinguish what keys were held down
when RESET or BREAK was pressed?)
The state of the SELECT, OPTION, and START keys can be read
at any time (because they are "console switches" as on the 2600).
Most other keys send an internal code along with the state of
the Control and Shift keys. It is not possible to detect Shift
or Control by themselves, or distinguish between the two Shifts.
esc 1 2 3 4 5 6 7 8 9 0 < > backspace
tab q w e r t y u i o p - =
a s d f g h j k l ; + * return
z x c v b n m , . /
space caps atari
I assume the keycodes are the same on all keyboards.
- All machines except the 400/800 have a HELP key. It acts
like the letter keys above (sends a keypress, along with
Control and Shift bits) but to a different memory address.
- Only the 1200XL has F1 F2 F3 and F4. They behave the same
way as the letter keys and HELP (only keypresses can be
detected, with Shift and/or Control). Only the 1200XL has
a software-controlled LED.
Thanks for your help,
-- Derek