Namco Pac-Man/Custom IC Pinouts

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Revision as of 06:05, 8 May 2023 by Lockster (talk | contribs) (added pinout diagrams of the custom IC's and a brief description of their function. Will describe their signals soon)
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The Namco Pac-Man logic board features a pair of Custom Integrated Circuits manufactured by Fujitsu for Namco. They're marked NVC285 and NVC284, respectively. Ideally to deter reverse-engineering and prevent piracy of the logic board. However this didn't prevent bootlegging of the hardware by other companies.

NVC285 - Z80 Sync Bus Controller

The NVC285 controls the passage of data between the Z80's CPU data bus (D0-D7) and the buffered data bus (DB0-DB7) to keep in sync with controlling the video and audio components of the board. 

         .---\/---.
  6M* -> |01    28| -- VCC
   1H -> |02    27| <- /CS
   2H -> |03    26| <- /M1
  DB4 <> |04    25| <> D4
  DB3 <> |05    24| <> D3
  DB5 <> |06    23| <> D5
  DB6 <> |07    22| <> D6
  DB2 <> |08    21| <> D2
  DB7 <> |09    20| <> D7
  DB0 <> |10    19| <> D0
  DB1 <> |11    18| <> D1
   CK <- |12    17| <- /WREQ
  R/W <- |13    16| <- /RD
  GND -- |14    15| <- /IORQ
         `--------'

NVC284 - VRAM Addresser

The NVC284 controls how the Tilemap and Color values in Video RAM are addressed to display the playfield. It is used to synchronize the Video and Work RAM with system timing, and to flip the playfield when in the game is in cocktail table mode. 

          .---\/---.
    2H -> |01    28| -- VCC
    4H -> |02    27| <- FLIP
    8H -> |03    26| -> AB0
   16H -> |04    25| -> AB1
   32H -> |05    24| -> AB2
   64H -> |06    23| -> AB3
  128H -> |07    22| -> AB4
 /256H -> |08    21| -> AB5
    8V -> |09    20| -> AB6
   16V -> |10    19| -> AB7
   32V -> |11    18| -> AB8
   64V -> |12    17| -> AB9
  128V -> |13    16| -> AB10
   GND -- |14    15| -> AB11
          `--------'

Likely due to the success of Pac-Man in the states, Fujitsu couldn't keep up with the supply for demand of these custom ICs. Therefore small circuit boards made up of discrete 74-series logic to replicate their functionality were often used as replacements. These replacements are common on Midway Pac-Man boards. This also made it easier for bootleg copies of Pac-Man boards to be distributed.


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