keyboard

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Thanks for the explanations.  A couple more questions, though:

If a parallel input is used, how does the keyboard (or PC parallel port
or whatever that's serving as a keyboard) signal the P21 system that
a key has been pressed?  There can't just be a parallel ascii character
presented to the P21 system; the system must also be notified that a key
has
been pressed.  Unless the P21 system simply looks for _changes_ in the
input pattern, and assumes the key is released when the input pattern
returns to all zeros or all ones on the 7 bits of parallel input... ?
What do you mean by "bitbanging" for serial input?  Is there a
synchronizing clock signal, or does it run at a set asynchronous rate
such as 9600bps?
I will be using the rom image "slow.rom" from the zip file "102roms.zip"
and will be placing the resultant eprom chip in the system exactly as
shown in the schematic in the manual.  I assume this will work.

>     Do not try to connect a PC keyboard.  First of all it uses
>     a funny clocked serial signal, and it outputs funny key codes,
>     not ascii.  
Thank you for the warning.  I'll go get my trusty Apple II keyboard
that reliably outputs simple ascii.

--Andrew