Namco Pac-Man/Custom IC Pinouts

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< Namco Pac-Man
Revision as of 08:06, 24 May 2023 by Fiskbit (talk | contribs) (Some formatting and wording improvements.)
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The Namco Pac-Man logic board features a pair of custom integrated circuits manufactured by Fujitsu for Namco, perhaps intended to deter reverse-engineering and prevent piracy of the logic board. However, this didn't prevent bootlegging of the hardware by other companies.

Pinouts

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
         `--------'

Discrete logic replacements

Likely due to the success of Pac-Man in the states, Fujitsu couldn't keep up with the demand for these custom ICs. Therefore small circuit boards with discrete 74-series logic replicating 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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