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Old 13th Apr 2018, 5:06 pm   #8
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: MK14 (Microcomputer Kit 14) PIC14

I remember noticing that the '240 didn't appear to have open collector outputs (as the original discrete transistor cathode drivers obviously did) but my PIC14 still doesn't have a keypad wired to it so I can't (yet) replicate the scenario you suggest to see if it has any repercussions in practice.

As it happens I can't think of any of the original example programs which required you press more than one key so this situation would rarely come up, but you are right to wonder what could happen. A two-finger typist might occasionally still be releasing one key as they hit another with the other finger.

Perhaps for anyone building one now, Karen's 'Third Way', retaining the transistors but adding capacitors would be the way to go.
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