Designed custom PDP-11 RAM with ChatGPT and EasyEDA

Dave W Plummer@davepl1968

I made my own RAM! And it almost works!

If you think regular RAM is expensive, try PDP-11 memory. It's like $1000 per megabyte if you can find it.

So, I set out to make my own. With ChatGPT in hand, we got busy in the EasyEDA designer. I've done PCBs before, but nothing this complicated.

We got the schematic done, the PCB laid out, routed, and the Bill of Materials ready for production. With the FPGA code saved away, I ordered 5 of the boards to test.

I’ve never flashed an FPGA before, so I bought an FT232H and wired it up.  I installed openFPGALoader and after a few false starts over compressed bitstreams, I managed to get it flashed.  All new territory for me!

After a bunch of bench testing, I ultimately put it in a backplane with an M8190.  And the good news is it shows up as both 4M of RAM and reserved space for the ROM.  The bad news is that access to any ODD memory location fails.  So I’ve got something that amazingly almost works end to end, but has a really fundamental problem.

So at this point, my RAM works, but only half as well as it should. I'll keep you up to date!