Re: Apple II's paddle 3 button

[mjmahon@aol.com (Michael J. Mahon)]

Steve (ground.ecn AppleII Librarian) wrote:

<snip>

>As many have pointed out, $c060 is the cassette input on older II's, and
>can be used as PB3 input, although IIRC the "state" is reversed from the
>PB inputs at $c061-$c063.  IE, if PB0-PB2 is normally off and momentarily
>on when a switch is pressed, PB3 is normally on and momentarily off when a
>switch is pressed.  I beleive the "Paddle-Adaple" (sp?) came with a mono
>plug to put into cassette port and then apple games could theoreticcaly
>provide full support for 4 paddles.  But I don't know if any games ever
>did this.

The cassette input is inverting, so anything sensed there will be opposite
in state to the pushbuttons.  However, the cassette input is also AC-coupled,
as was pointed out, so DC sensing is impossible.

In the IIgs, there is no inverting opamp and no coupling capacitor, so
PB3 has the same "polarity" as the first three buttons.

It should be noted that PB2 (shift key mod) and (on the IIgs) PB3 are
both pulled up to +5, so they should be "actuated" by a switch that
grounds them, rather than connecting them to +5.  On the //e and
//c, PB0 and PB1 are pulled down to ground (in the keyboard), so
those switches operate by connecting them to +5.

What began as a simple, homogeneous scheme in the Apple ][
and ][+, evolved into a somewhat byzantine arrangement over
the years, capped off (!) by the installation of EMI- and speed-
reducing capacitors in the Platinum models.

-michael

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