After a year without working on a retro project I decided to start a new project with a intel 80286 that I had found in a parts bin at my workplace. First thing was to read on the subject then I had come across rehsd 80286 project on Youtube (Playlist here) that inspired me to realy start working on it.

Here’s the ressources that I had read up to this point :

Clock circuit

I built a simple circuit board with some 555 timer to generate the clock, this board can generate a variable clock with a variable resistor. There is more ICs on this board that I do not use right now, in the future a want to use this to generate a single step clock with the button.

Now with the Clock Circuit done, I needed to split all the pins from the 286 CPU to be able to use it on a breadboard. So I built a breakout board from a small protoboard and added :

  • A 40 pins header on each sides.
  • LED Bargraph for the S0, S1, COD/INTA and M/IO signals.
  • Pull up and pull down resistors.

Finally I can now try to free-run the CPU with hardcoded NOP (a instructionto do absolutly nothing) and more LED Bargraph to visualize if the address bus is incrementing with each NOP operations.

Everything is working as planned, the CPU is executing the NOP instructions then increment the address lines by one and executing a NOP again in a loop.

At that point I began to realize that I needed to order some ICs to help me generate some control signals for the CPU. So I ordered the following ICs, as per the intel documentation I need :

  • 80284 – Clock driver chip to generate the CLK, RESET and PCLK signals.
  • 80288 – Bus Controller chip to generate the ALE, MRDC, MWTC, IORD and IOWR signals.
  • 74HCT245 – For the Data Bus transceivers
  • 74HCT573 – For the Address Bus transceivers

To be continued …

Dom