Contains the images for the Williams Decoder PROMs
for Defender, Stargate, Robotron, Bubbles, Joust, Sinistar,
etc.

You can hack a 2716 onto the board, you need to copy
the image 4 times into the chip.

Pinouts:
       ____  ____
  A7 -|1   \/  24|- Vcc
  A6 -|2       23|- A8
  A5 -|3   V   22|- Vcc
  A4 -|4   i   21|- /CE1
  A3 -|5   d   20|- /CE2
  A2 -|6   e   19|- CE3
  A1 -|7   o   18|- CE4
  A0 -|8       17|- D7
  D0 -|9   P   16|- D6
  D1 -|10  R   15|- D5
  D2 -|11  O   14|- D4
 Gnd -|12  M   13|- D3
      '----------'

       ____  ____                 ____  ____
  A7 -|1   \/  24|- Vcc      A7 -|1   \/  24|- Vcc
  A6 -|2       23|- A8       A6 -|2       23|- A8
  A5 -|3       22|- A9       A5 -|3       22|- A9
  A4 -|4       21|- Vpp      A4 -|4       21|- A11
  A3 -|5   2   20|- /OE      A3 -|5   2   20|- Vpp
  A2 -|6   7   19|- A10      A2 -|6   7   19|- A10
  A1 -|7   1   18|- /CE      A1 -|7   3   18|- /CE
  A0 -|8   6   17|- D7       A0 -|8   2   17|- D7
  D0 -|9       16|- D6       D0 -|9       16|- D6
  D1 -|10      15|- D5       D1 -|10      15|- D5
  D2 -|11      14|- D4       D2 -|11      14|- D4
 Gnd -|12      13|- D3      Gnd -|12      13|- D3
      '----------'               '----------'

The differences are 18 - 22.

Pin Video Decoder 2716 2732 
18 CE4 /CE /CE 
19 CE3 A10 A10 
20 /CE2 /OE Vpp 
21 /CE1 Vpp A11 
22 Vcc A9 A9 

Looking at the CPU board we can see that for the video decoder:

Pins 18 and 19 are both tied high by a common resistor
Pins 20 and 21 are tied low
Pin 22 is tied high

If we want to use an EPROM we need:

Pin 18 must be low (this is chip enable for a 2716 and 2732)
Pin 19 can be high or low
Pin 20 must be low for a 2716 and can be low for a 2732
pin 21 can be high or low
pin 22 can be high or low

The only pin to alter is 18, this is presently tied high by
a 4.7k resistor but we want it low. Remove the resistor, you
will be left with 2 holes where the resistors legs were.

Fill the hole at the +5v side with solder.
Run a jumper from the hole at the PROM side to GND. This will
also tie pin 19 to GND but this doesn't matter.

Drop in a 2716 or 2732 filled with multiple copies of the
video decoder data.  Use 250ns parts or faster.



