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ASTRO INVADER (Stern, 1980)
---------------------------

Filenames of the form "ASTINVAD.xx", where "xx" is the 
marking on the ROM.  There are no position indicators 
on the board, so ASCII diagrams have been included in
this document to aid in parts placement.

Astro Invader comes in a card cage with a three-slot 
backplane.  There is some simple circuitry on the 
backplane, but the game itself resides on three boards:

1) Top Board
   - This board contains two 8255s, a row of 7 trim pots,
     and a heat-sinked LM1877.  There are no ROMs on this board.
   - With the backplane 44-pin edge connector facing your left,
     the parts are located as follows:
   - There are two pairs of jumper posts near one of the 8255s.
     I've named them J1 and J2.  I don't know what they do, but
     on my set, J1 was connected and J2 was not.
   - The trim pots are volume controls for the individual sound
     effects used in the game.  The pot nearest the heat sink
     controls the overall volume.  Audio output is strange, 
     being two pins with opposite waveforms laid on top of a 
     +10VDC offset.

       .-----------------------------------.
      _| POT POT POT POT POT     POT  HEAT |  J1 - Connected
     |                                SINK |
     |                                     |  J2 - Not connected
     |                                     |
     |                                     |
     |                                     |
     |_   8255      8255                   |
       |              J1   J2              |  
       `-----------------------------------'

2) Middle board
   - This board contains seven 2708s and a Z80 microprocessor.

       .-----------------------------------.
      _|    _    _    _                    |
     |     | |  | |  | |                   | 
     |     |3|  |5|  |7|       ___         |  ROMs: 2708 (e.g. HN462708)
     |     |_|  |_|  |_|      |   |        |
     |      _    _    _       | D |        |  RAMs: Two 2114-3s 
     |     | |  | |  | |      | 7 |        |
     |     |2|  |4|  |6|      | 8 |        |  CPU: D708C (Z80 CPU)
     |     |_|  |_|  |_|      | 0 |        |
     |      _                 | C |        |  XTAL: 2.0 MHz
     |     | |   R    R       |___|        |
     |_    |1|   A    A              XTAL  |
       |   |_|   M    M                    |  
       `-----------------------------------'

3) Bottom board
   - This board contains one 2708 EPROM and two 8-chip banks 
     of Mitsubishi "M5T4044P-45" RAM.  The chips also have a
     marking of "M58754".  I haven't a clue what these are,
     other than that they're obviously very small RAMs.

       .-----------------------------------.
      _|     RAM RAM            XTAL       |
     |       RAM RAM                       |  ROM: 2708 
     |       RAM RAM          ROM "C"      |
     |       RAM RAM                       |  RAM: M5T4044P-45
     |       RAM RAM                       |       (M58754?)
     |       RAM RAM                       |  
     |_      RAM RAM                       |  XTAL: 4.9155 MHz
       |     RAM RAM                       |  
       `-----------------------------------'


Filename.rom  Type  Csum
------------  ----  ----
ai_cpu_1.rom  2708  89db
ai_cpu_2.rom  2708  8f82
ai_cpu_3.rom  2708  59a2
ai_cpu_4.rom  2708  21ca
ai_cpu_5.rom  2708  55bc
ai_cpu_6.rom  2708  2b8f
ai_cpu_7.rom  2708  714b
ai_vid_c.rom  2708  d79e