Kevin Greene wrote:
What purpose does the resistor serve? I know I've shorted those switch and +5V pins with a wire for testing and I seem to remember it worked fine without damaging anything that I noticed (this was on a II+).Michael J. Mahon wrote:+5v >----------+ |- Switch PB0 >----------+ \ 220 ohms Gnd >----------+
Kevin: The resistor charges and discharges the input.This resistor is to pull the paddle to a definate low potential or zero volts when the switch is inactive. If you only have the switch and 5V the input can be left 'floating' and could randomly (or predictably) be misread as having the switch still applied.
Oh, and personally I'd duplicate this circuit for a second Apple II and use a Double pole/ momentary switch and keep the apple electrons isolated. :)
A1 A2
5v --- --- 5v
|-S-|
PBx--- ---PBx
R R
0v --- --- 0v
Thankx,
Ed