NEO-257: Difference between revisions
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[[File:neo-257.jpg|right|thumb|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. | 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. | Used in dual slot MVS systems to select one of the two [[C ROM]] (and S ROM ?) buses. | ||
Revision as of 12:47, 19 July 2012
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.
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)