[GTALUG] [Fwd: Re: Hardware Hack - help needed]

phiscock at ee.ryerson.ca phiscock at ee.ryerson.ca
Tue Apr 11 13:14:28 EDT 2017


> Back in the days of the Commodore PET, I wanted to convert the keyboard
>> into Dvorak layout. Nowadays, I'd find the keyboard translation table,
>> edit that and blow a new ROM.
>
Usually keyboards are wired as a matrix with the lines in the cable
representing the X and Y scan lines and each switch at the junction of a
pair of scan lines. The output scan lines have resistor pullups so they
are normally all in the high state.

One set of 'input' scan lines  (say X) is then sequentially made LOW and
the other set of scan 'output' lines is read in and decoded. When a switch
is closed, one output line will go low when some specific input line is
activated. This scan operation can happen very fast, so the keyboard is
repeatedly scanned at 60 times a second or faster. (This matrix
arrangement minimizes the number of required connections to the keys.)

Then a computer decodes the XY coordinates into a key code. This would not
be difficult to do with an arduino type processor: you'd use the output
parallel port lines as the keyboard output scan lines, and another
parallel input port as the input scan lines. Send the decoded information
out the Arduino usb port.

We used to give this to our EE students at Ryerson as an exercise in
assembly language programming.

Peter

-- 
Peter Hiscocks
Syscomp Electronic Design Limited, Toronto
http://www.syscompdesign.com
USB Oscilloscope and Waveform Generator
647-839-0325



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