On Sat, 30 May 1998, Allison J Parent wrote:
> Things you cant do with a software scanned keyboard:
>
> Key pressed interrupt, if the cpu doesn't scan the keyboard it cannot
> sense activity. It takes some chips extra then to sense any key pressed
> and cause a interupt to initiate a keybard scan and debounce routine
> to see what happend.
That's OK. The Apple was only able to sense one keypress at a time
anyway. In fact, you still had to scan an address to see if a key was
pressed (location $C000). If the hi-bit was on, a key was pressed. After
you read the key, you would have to then access (read or write) location
$C010 in order to reset the keyboard strobe. If you didn't do that, the
keypress location hi-bit would remain set. However, the value would
change for each new key pressed, but you could still only read one
keypress at a time. It was hokey and funky but you leanred to work around
it, and besides not having a type-ahead buffer (unless you kludged one in
software) it worked fine.
> The keyboard chips did n-key rollover and buffered at least one
> keystroke.
I don't know what you mean by n-key rollover. But it only buffered on
keystroke. If you pressed another key before you scanned the keyboard
strobe, you lost the previous keypress.
Sam Alternate e-mail: dastar_at_siconic.com
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Received on Sat May 30 1998 - 23:30:07 BST