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ISA 8-bit Backplane
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README.md

ISA 8-bit Backplane

Compact ISA 8-bit Backplane board

Introduction

This backplane was designed as a smaller version of Micro ATX ISA Backplane. It can be used to build a compact IBM PC/XT compatible system using the Micro 8088 processor board, and the 8-bit ISA cards that I've designed: ISA Super VGA, ISA Floppy Disk and Serial Controller, XT-CF-Lite, ISA OPL2.

ISA 8-bit Backplane V1.0 Assembled Board

Specifications

  • 7 ISA 8-bit (62 pin) slots
  • ATX power supply connector, and ATX power control circuit
  • Bi-color activity LED, that changes the color when the processor is executing the code (the color changes every time A7 address line changes its value)
  • The form factor is (mostly) compatible with ATX / Micro ATX
  • Pads for optional termination resistors

Hardware Documentation

Schematic and PCB Layout

Schematic - Version 1.0

PCB Layout - Version 1.0

Building Insturctions

Please refer to Building Instructions page for detailed instructions.

Jumpers, Connectors, and Switches

P1 - ATX power connector

Pin Description Pin Description
1 +3.3V power supply (not used) 11 +3.3V power supply (not used)
2 +3.3V power supply (not used) 12 -12V power supply
3 GND 13 Ground
4 +5V power supply 14 Power supply ON signal
5 Ground 15 Ground
6 +5V power supply 16 Ground
7 Ground 17 Ground
8 Power good (not used) 18 -5V power supply (not used)*
9 +5V standby power supply 19 +5V power supply
10 +12V power supply 20 +5V power supply

Note: -5V is not provided by most ATX power supplies. It is generated using an on board voltage regulator instead

P2 - Power Switch connector

Pin Description
1 Ground
2 Power ON signal

P3 - Power LED connector

Pin Description
1 LED+
2 Ground

SW1 - Power Switch

Press SW1 to turn power on or off. The SW1 is connected in parallel with P2

Bill of Materials - Version 1.0

ISA 8-bit Backplane project on Mouser.com - View and order all components except of the PCB.

ISA 8-bit Backplane project on OSH Park - View and order the PCB.

Component type Reference Description Quantity Possible sources and notes
PCB ISA 8-bit Backplane PCB - Version 1.0 1 Refer to the RetroBrew Computers Board Inventory page for ordering information, or order from a PCB manufacturer of your choice using provided Gerber or KiCad files
Integrated Circuit U1 74HCT74, DIP-14 package 1 Mouser 595-SN74AHCT74N
Integrated Circuit U2 74HCT14, DIP-14 package 1 Mouser 595-SN74AHCT14N
Integrated Circuit U3 LM7905C -5V voltage regulator 1 Mouser 512-LM7905CT
IC Socket U1, U2 DIP-14, 300 mil socket 2 Mouser 517-4814-3000-CP
LED D1 3 mm, blue LED indicator 1 Mouser 696-SSL-LX3054USBD
LED D2 3 mm, bi-color red/green LED indicator 1 Mouser 696-SSL-LX3054IGW
Diode D3, D4 1N4148 2 Mouser 512-1N4148
Tactile Button SW1 6 mm tactile button, straight 1 Mouser 653-B3F-1000
Connector P1 20 pin ATX power connector 1 Mouser 538-46015-2006
Connector P2, P3 4 pin header, 2.54 mm pitch 2 Mouser 649-68002-104HLF
Connector BUS1-BUS7 62 pin card edge connector, 2.54 mm pitch 7 Mouser 571-6-5530843-5
Capacitor C1 - C19 10 uF, 16V, MLCC, 5 mm lead spacing 19 Mouser 810-FG28X5R1E106MR06
Capacitor C20 1 uF, MLCC, 5 mm lead spacing 1 Mouser 810-FG28X5R1H105KRT0
Capacitor C21, C22 0.1 uF, MLCC, 5 mm lead spacing 2 Mouser 594-K104K15X7RF53H5
Resistor R1, R2 10 kohm, through hole 2 Mouser 291-10K-RC
Resistor R3 1 kohm, through hole 1 Mouser 291-1K-RC
Resistor R4 - R7 470 ohm, through hole 2 Mouser 291-470-RC
Resistor Array RR1 - RR5 do not populate Optional, should not be populated
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