Difference between revisions of "NEO-257"

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m (enable info)
m (some more info from my 2F)
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*Select: Output A if LOW, B if HIGH.
 
*Select: Output A if LOW, B if HIGH.
 
*Some pins marked as ground could be "enable" pins
 
*Some pins marked as ground could be "enable" pins
**35 is active high enable atleast for Y8~Y15
+
**35 is active high enable for entire chip
**33 is active low enable atleast for Y8~Y15 (confirmed from NEO-257 connection on a 2 slot). In the example from the pic it appears to be hardwired to always be enabled.
+
**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)
 
[[Category:Chips]]
 
[[Category:Chips]]

Revision as of 07:46, 9 May 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.

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)