I had a few projects planned doing some retro-computing.

In my electronics boxes I have both new old stock and recycled processors:

  • 6502
  • 65sc02
  • 65sc816
  • 68008
  • 68000
  • 68010
  • 8086 (oh my, how did that happen?)

So over the christmas holidays I tried to finally get started. With getting a 68008 free-running. My thought process was that when I got that one running, and a basic monitor to access the system from the outside, I could switch to the 68000 or the 68010. The reasoning being that those two are much bigger physically and require a 16-bit memory system - that’s two EEPROMs and two RAM chips. Which is twice the effort.

Well, I couldn’t get the 68008 to work in free-running mode. Possibly because my chips are dead (didn’t try them all, so I don’t know), possibly because I forgot one of the many many signals this processor uses to communicate with the outside world.

So I switched to the 68000. Still no luck.

Today I tried the 65sc02, and none of them works. What did work - after I pulled the /ABORT pin high - was a 65sc816. So that is probably now becoming the base of my single board computer project. On startup, the 65sc816 behaves pretty much like a 65sc02 anyway.

But wait, there’s more

Using the 65sc816 opens up some extra opportunities, “16-bit mode” (or native mode, as real 816ers call it), a 24-bit address bus (done by multiplexing the databus and the upper 8 address bus bits - a bit like the 68008, come to think of it) and the simple fact that my 65sc816s seem to work. No more need for SWEET16 since we can do 16 bits native.

So yes, I’m very pleased for now.

The next step(s)

So now I have to do all of this:

  • real power-on reset (right now I only have a button)
  • address decoder
  • get a basic RAM/ROM subsystem running
  • get some I/O running (I2C would be nice)
  • get wozmon bastardized into that system
  • get a BASIC running (BBC Basic?)
  • program a FORTH
  • micropython? Do I dare port that to the 65sc816?
  • flash memory (got some nice 29F1615s just waiting)
  • SD-card interface?
  • RTC?
  • getting all of that a bit more permanent, that is, perfboard instead of breadboard.

Oh, and:

  • make some pictures
  • make some videos