NEO-257

NEO-257 chip found on a MV2B MVS board.

Quadruple 74HC257 2-to-1 multiplexer with common select line, making 16 switches in one chip. Used in dual slot MVS systems to select one of the two C ROM (and S ROM ?) buses.

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

Pinout

Information provided by Channelmaniac.

File:Neo-257 pinout.png

OpenOffice Draw file: File:Neo-257.odg

• A*,B*: Inputs
• Y*: Outputs
• Select: Output A if LOW, B if HIGH.
• Some pins marked as ground could be "enable" pins
  • 35 is active high enable for entire chip
  • 18 is active low enable for Y0~Y7 (comes from "SYSTEMB" on a MV-2F and used to control /OE for FIXD0~FIXD7 from cart)
  • 33 is active low enable for Y8~Y15 (comes from "SDROM" from NEO-D0 to output cart M1 data to Z80)