Latest revision as of 02:40, 28 November 2018


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

Repair

The NEO-257 is known to fail on damaged MV2B and MV2F boards. If some pins are dead, they can be lifted and wired to a 74LS257. These instructions only work for the MV2B chips at L4 and K4.

Wire the NEO-257 data inputs to any of the 74LS257 input pairs (in correct order).
Wire the 74LS257 output to the output pad.
Wire the NEO-257 pin 17 to the 74LS257 select input.
Wire power, the 74LS257 output enable to ground, and don't forget to ground the unused inputs if using a CMOS part.

Pinouts

Information provided by Channelmaniac. Pins 2 and 3 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

SYSTEM and SYSTEMB might be reversed ?

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

@@ Line 1: / Line 1: @@
-[[File:neo-257.jpg|right|thumb|NEO-257 chip found on a [[MV2B]] MVS board.]]
+{{ChipInfo
+|picture=Neo-257.jpg
+|pkg=QFP64R
+|manu=fujitsu
+|date=1990 ?
+|gates=
+|used_on={{PCB|MV2B}}...
+}}
-Quadruple 74HC257 2-to-1 multiplexer with common select line, making 16 switches in one chip.
+Four "74HC257" quad 2-to-1 multiplexers with a common select line and separate output enables.
-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]] ?
+Makes 16 switches in one chip (32 inputs, 16 outputs).
-== MV2B @ K4 pinout==
+Used in dual slot MVS systems to switch between carts.
+Select signal comes from one of the "SLOT" outputs of {{Chipname|NEO-F0}} ?
+=Internal logic=
+'''This is NOT verified'''.
+See https://github.com/neogeodev/SNKVerilog/tree/master/NEO-257
+=Repair=
+The NEO-257 is known to fail on damaged [[MV2B]] and [[MV2F]] boards. If some pins are dead, they can be lifted and wired to a 74LS257. '''These instructions only work for the MV2B chips at L4 and K4'''.
+* Wire the NEO-257 data inputs to any of the 74LS257 input pairs (in correct order).
+* Wire the 74LS257 output to the output pad.
+* Wire the NEO-257 pin 17 to the 74LS257 select input.
+* Wire power, the 74LS257 output enable to ground, and don't forget to ground the unused inputs if using a CMOS part.
+=Pinouts=
+Information provided by Channelmaniac. '''Pins 2 and 3 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.
+[[File:Neo-257_L4_pinout.png|512px]]
+OpenOffice Draw file: [[File:neo-257_L4.odg]]
+== MV2B @ K4==
+Used to switch the lower 16 bits of the sprite graphics bus.
 [[File:Neo-257_K4_pinout.png|512px]]
@@ Line 12: / Line 58: @@
 OpenOffice Draw file: [[File:neo-257_K4.odg]]
-== MV2B @ J11 pinout==
+== MV2B @ J11==
+SYSTEM and SYSTEMB might be reversed ?
 [[File:Neo-257_J11_pinout.png|512px]]
@@ Line 18: / Line 66: @@
 OpenOffice Draw file: [[File:neo-257_J11.odg]]
-== Pinout ==
-Information provided by Channelmaniac.
-[[File:Neo-257_pinout.png|512px]]
-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]]
+[[Category:Repairs]]

NEO-257: Difference between revisions