Thread: Ortonview PCB
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Old 29th Jun 2021, 7:59 pm   #20
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,482
Default Re: Ortonview PCB

Well, I was suggesting putting the resistors in series with the pulldown switches rather than in series with the 8154 port pins, so their only function is to stop 8154 pins which are in output mode (Or indeed Flag outputs, which Tim likes to use) being shorted directly to GND in the event that any pulldown switch gets moved to the closed position.

Obviously the ratio of the switch series resistors and the pullup resistors will have to be such that closing a switch still imposes a valid logic 0 level when there is nothing else (8154 output, Flag output) driving the line to 5V or 0V.

Don't worry too much about the actual values, just provide somewhere to insert them or insert links and we will experiment for best value.
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