8-bit CPU: design the PCBs

The idea is clear, now the hard part: design the boards.

I've been long time CatSoft Eagle user, but since they've been acquired by Autodesk, things have gone downhill. It did not even wanted to start on my machine (I use Linux as my primary OS). Well, so long and thanks for all the fish! KiCAD seems to be popular in the community, let's learn something new.

As planned before, I started with ALU module. The schematics part was quite easy, there are no space constraints when drawing that. PCBs on the other hand...

After board outline was set and connectors placed, it started to feel quite terrifying. Can I really fit ALL THAT on this small board? Eventually I did...

Next I have to route the tracks, a lot of them. Felt a little lazy to do it all by hand and wanted to see what autorouter produces. Turns out, there is no such feature in KiCAD. Everybody appears to to hate autorouters!

There was an option to export the board, autoroute it in FreeRouting and then import it back. The board was complicated enough and autorouter struggled to find a solution. Eventually it did, but I had to move chips around, swap gates and input pins. Not sure if it saved me any time.

ALU done, next Register and Flags. Boards are less complex, but it still took some effort to do them. I still had some hopes for autorouter's help, but it was not easy anyway. Not sure if I'll bother with it next time.

Here's how the register will look like when it's done (front and back).

 
 
 

It actually takes quite an effort to design a board like this, especially when space is tight. Well, I chose those constraints for myself.

I decided also to design a PCB version of the EEPROM burner - as a shield for Arduino Uno. That should be more stable and convenient to use, and I'll be able to reclaim the breadboard. Added additional headers for external connections - it should double as a control logic for module testing. One more extra - a PLCC socket for smaller footprint EEPROMs.

Ordered the boards at JLCPCB, should get them quite soon. Hopefully, the parts from Farnell will arrive roughly at same time.

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