NEO-257: Difference between revisions

Revision as of 10:13, 29 September 2016

Four "74HC257" quad 2-to-1 multiplexers with some common select lines and 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 ?

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

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

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

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

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

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

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

@@ Line 39: / Line 39: @@
 == Pinout ==
-Information provided by Channelmaniac.
+Information provided by Channelmaniac. '''Some pins marked as GND could be "enable" pins'''.
-[[File:Neo-257_pinout.png|512px]]
+* 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
-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)
 [[Category:Chips]]