Re: Game port

[Rubywand <rubywand@swbell.net>]

David Empson writes ...
> 

 ....

> 
> A final note: the IIc does not have a button 2 input, and its button 0
> and 1 inputs are not quite the same as other machines, since they double
> up as mouse detection and button signals (which use the opposite logic -
> connecting to ground when the mouse is plugged in or the button is
> pressed).

     The last statement is a bit hard to follow. If the normal (when
plugged in) mouse button status is at Gnd, how can pressing a button
bring the line to Gnd? Do you mean that plugging in the mouse puts Mouse
ID (PB1) at Gnd and that Mouse Button (PB0) is normally at "1" until it
is pressed?


     Regarding pinout of 9-pin A2 mouses, is the following correct?

>>

The IIe/IIc/Mac Plus mouses can plug into the //c or IIc+ Game/Mouse
port or, on a IIe, into the 9-pin socket of a Mouse Card. When plugged
into the //c or IIc+, several pins are redefined for use with a mouse.


DB-9 Female Socket (on computer)
  ,---------------------.
  \  5   4   3   2   1  /
   \   9   8   7   6   /
    `-----------------'

   Mouse         Usual Game Port Function

1  MOUSE ID      Pushbutton 1
2  +5V           +5V
3  GND           GND
4  XDIR          Game Control 2 or PDL2 (Joystick-2 X-axis)
5  XMOVE         Game Control 0 or PDL0 (Joystick-1 X-axis)
6  n.c.          Pushbutton 2 (not on //c)
7  MOUSE BUTTON  Pushbutton 0
8  YDIR          Game Control 1 or PDL1 (Joystick-1 Y-axis)
9  YMOVE         Game Control 3 or PDL3 (Joystick-2 Y-axis)

<<

     Does the IIc+ also omit a connection for PB2?

> 
> You cannot reliably put a TTL level into a IIc.  The only officially
> supported input combinations are a switched +5V with pulldown (as on
> earlier machines), or a similar transistor configuration (fully
> saturated PNP, with Vce <= 0.3V, and current into the IIc >= 30 mA,
> according to the techincal reference).
> 
> The IIc manual specifically excludes a schottky gate output, switched
> ground through a transistor (open collector), and emitter follower
> transistor configuration.

     It seems like about the only way to exclude Open Collector is for
the //c PB inputs to include a resistor going to Ground. Something like
1200 Ohms would let you use standard A2 joysticks without sucking too
much more current during a button push.

     To interface such an input to TTL, you would be stuck with
something like ...

            +5V
              \ E
               \ |        about 1k
                 |--B-----/\/\/\--------<--- Output from TTL gate
     PB input  / |
---------o----/ C  PNP Transistor
         |
         Z
         Z
         |
        Gnd

i.e. your saturated PNP transistor.

     Would the above circuit work on a //c?



Rubywand