I want to implement interrupts next. This is a topic I’ve shied away from up until this point (I just wanted to get something simple working) but I now feel my computer is stable enough for me to look at.
I knew I’d need to modify my CPU board … so I figured I might as well design a new board and get OSHpark to manufacture it.
The only “new” facility it provides is the addition of pins designated for IRQ and NMI. But because I’m now working with double-sided boards and much thinner tracks, I’ve managed to make the new board much smaller.
Now feels like a good time to show how my prototyping has changed over time.
Here’s my first CPU board, done with stripboard and lots of loose wire:
It’s a mess … but it works.
Here’s my second board, which is a single-sided board etched on my CNC:
It’s quite big because I tend to err on the fatter side when designing tracks which a drill is going to etch around. The two blue wires you can see on the underside were my quick attempt to add NMI and IRQ lines … before I decided just to replace the entire board.
And here’s my new board; double-sided, much finer tracks densely packed together, with silk layers and daft graphics:
(I intend to write a separate article about the graphics, because I had a lot of fun writing the code that adds it to the PCB data.)
I’m quite pleased that the board you’d expect to be amongst the most complicated of the computer (it’s the CPU board, after all) is actually one of the smallest!