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SubjectRe: Keyboard error
On 11 Aug 1997, Linus Torvalds wrote:

[...SNIP...]
>The keyboard signals the error, and there is nothing the driver can do
>about it. So yes, the answer is "don't do that, then".
>
>The deeper reason for the error can be found in how the keyboard
>physcially scans which keys are pressed. For reasons of economy, most
>keyboards have a simple "scanning array" where a keypress shorts one
>array corner (*). Depending on how the array is set up, pressing
>multiple keys will not always work - and the exact keys that result in
>breakage depend on the topology of the scanning array.
>
>Many multi-key-presses will create a "shadow key press" (so when you
>press three keys, the keyboard controller will actually think that
>you're pressing four keys, and I suspect that the keyboard controller
>just notices that two keys changed simulataneously and will consider
>this an error.
>
>The keyboard array is usually set up in such a way that the "normal"
>keys that are often pressed together (alt, shift, cursor keys etc)
>create as few of these shadows as possible, but you've obviously found
>one of them. I suspect that you'll easily find more by just pressing
>lots of keys at the same time..
[...SNIP...]
>
> Linus
>

Linus is on the right track here, basically some more expensive keyboards
can take upto 7 keypresses (or more) at once, I found this out on a
friends keyboard, two players on one computer/keyboard setup, and
generally on cheap keboards you can get away 3 keypresses before you get a
keyboard "lock", does anybody remember how DOS/BIOS complains:
<bleep><bleep><bleep><bleep>....
My keyboard does 6 keys bofore it stops sending anything (no errors,
about AUS$100)

---------------------------------------
"When all of your wishes are granted,
many of your dreams will be destroyed",
Man That You Fear - Marilyn Manson
mabs@netdig.com.au
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