Re: Apple II's paddle 3 button

[mspangler@gemsi.com (Michael Spangler)]

Stefano Priore <stefano.priore@inwind.it> wrote in message news:<tij8ob.ru1.ln@127.0.0.1>...
> Michael J. Mahon <mjmahon@aol.com> wrote:
> > Stefano Priore asked:
>  
> >>To which memory location is paddle 3's button mapped? Some sources seem
> >>to imply that it's mapped to $c064, but according to others this switch
> >>reads joystick #1's X axis...
>  
> > There is no "official" relationship between Paddle 3 ("GC3") and a
> > particular pushbutton, since there are 4 paddle inputs and only
> > 3 pushbutton inputs.
>  
> > The third pushbutton input, usually referred to as PB2 but called
> > "pb3" on p.79 of the Reference Manual, is read at location $C063.
> 
> OK, now I see what confused me. But does this mean that Apple II's
> hardware can't read the status of the fourth pushbutton (PB3)?

There is no fourth pushbutton on a IIe or IIc. There is a fourth
button on a GS, which is often called PB3, and is at $C060, otherwise
known as the cassette input. The line is available on the internal 16
pin dip connector only.

Now, you can short a capacitor (C11) on a IIe, and get a DC TTL signal
to the $CO60 pin, and use it as a pushbutton input. I'm not sure, but
I think the op-amp would work as a buffer so that you could read a 12V
signal and not poof anything important.  I don't know enough about
op-amp circuits to say for sure. But since capacitors block DC, C11
has to go.

So, on a GS, the official list is $c060, PB3; C061, PB0; $C062, PB1;
$C063, PB2.
on a stock IIe, $C060 is the cassette input. The others are the three
(3) pushbuttons.

Hope this helps.