Very early Tomy game.  The VFD itself is cyan but there's a green filter over it
with a very hard to see tennis court printed on it.  I made the graphics on the svg
green to reflect this.

Nothing too special except the CPU's operating frequency is changed to control the
difficulty level!

Practice and pro2 run the oscillator at 360KHz, pro1 runs it at 260KHz.

The control buttons are multiplexed in a somewhat odd scheme:

pins 12/13 of the CPU (PE0, PE1) connect through diodes to various buttons. low enables
a particular set of buttons.  high disables it.

ports A and B are pulled high, and then pressing a button pulls the input(s) low if
the corresponding player button enable output is low.



Since the buttons are not really marked per se, here's a lame ASCII drawing:

(P1/P2 = player, S = serve button)


       P2A  P2C  P2E       P1E  P1C  P1A
P2S    [ ]  [ ]  [ ]       [ ]  [ ]  [ ]  P1S
( )                                       ( )
       [ ]  [ ]  [ ]       [ ]  [ ]  [ ]
       P2B  P2D  P2F       P1F  P1D  P1B



The practice/pro1/pro2 switch makes an electrical connection on the matrix when in the "practice" position only.

The 1player/off/2player switch makes an electrical connection on the matrix when in the "2player" position only.