NEO-257

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Revision as of 23:09, 29 September 2016 by Furrtek (talk | contribs) (→‎MV2B @ J11)
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Package QFP64R
Manufacturer
First use 1990 ?
Used on MV2B...

Four "74HC257" quad 2-to-1 multiplexers with a common select line and separate output enables.

Makes 16 switches in one chip (32 inputs, 16 outputs).

Used in dual slot MVS systems to switch between carts.

Select signal comes from one of the "SLOT" outputs of NEO-F0 ?

Internal logic

This is NOT verified.

See https://github.com/neogeodev/SNKVerilog/tree/master/NEO-257

Pinouts

Information provided by Channelmaniac. Some pins marked as GND could be "enable" pins.

  • A*, B*: Inputs
  • Y*: Outputs
  • 17 SELECT: A if low, B if high
  • 18 is an active low output enable for Y0~Y7
  • 33 and 34 are probably ORed together to provide an active low output enable for Y8~Y15
  • 35 is an active high enable for entire chip

MV2B @ L4

Used to switch the upper 16 bits of the sprite graphics bus.

OpenOffice Draw file: File:Neo-257 L4.odg

MV2B @ K4

Used to switch the lower 16 bits of the sprite graphics bus.

OpenOffice Draw file: File:Neo-257 K4.odg

MV2B @ J11

Used to switch between the onboard SM1 ROM / game M1 ROM, and onboard SFIX ROM / game S ROM.

SYSTEM and SYSTEMB might be reversed ?

OpenOffice Draw file: File:Neo-257 J11.odg