8088 Motherboard PC Compatible

Introduction:

This is my attempt at making a PC compatible motherboard. My first prototype board fits into a IBM 5150 case. Due to the availability of cases and power supplies I decide to go with a more modern approach. I am working on a motherboard on an ISA card.

Why an ISA card?

An ISA card is compact and allows for a more universal design. There is not a need for the user to have any specific case or power supply.

Build Objective:

  • Compatible with standard off the self ISA cards

  • Fits into a modern ATX case

  • Uses ATX or XT power supply

  • IO ports are compatible with IBM PC

Motherboard components:

  • 8088 or V20 Processor

  • 8259 Programmable Interrupt Controller

  • 8253 Programmable Interval Timer

  • 8237 Programmable DMA Controller

  • 8255 Programmable Peripheral Interface

  • Plugs into ISA back plane

  • 512k RAM

  • 32K ROM / 32K BIOS RAM

What currently works or still needs tested

  • 32k ROM, 32k upper RAM, and 512k RAM tested and seems to be correctly mapped

  • 8284 system clock works modified from original prototype

    • CLK 33% crystal works only connected to processor

    • PCLK 50% CLK works only connected to 8237 and 74LS74 div in half for system timer

    • OSC connected to ISA BUS not tested

    • ISA CLK 50% OSC not tested

  • 8259 interrupt controller seems to be working with no issues

  • 8253/53 system timer

    • IRQ0 tested and works

    • DRQ0/Refresh is connected but not tested

    • Speaker needs tested

  • 8237 DMA tested seems to work as designed. *8257 doesn't work

    • 74LS760 DMA register tested and works

    • 74LS573 DMA A8-A15 tested and works

  • 8255 keyboard port tested and works