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.
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.
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
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
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
System timer 0 connected to IRQ0
8253/53 system timer
IRQ0 tested and works
DRQ0/Refresh is connected but not tested
Speaker works
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