Z8 SBC
From neurotica.com
This tiny board was designed to exercise and explore the capabilities of Zilog's Z8 BASIC interpreter. This interpreter was originally shipped with the Z8671 processor, which is a Z8 with an on-chip mask ROM.
Note that the Z8 bears no relation whatsoever to the popular Z80, other than the fact that they're both Zilog products. There seems to be a great deal of confusion about this. The Z8 is a register file-based architecture which is optimized for microcontroller applications. This architecture lives today in Zilog's eZ8 and Z8 Encore! product lines. Z8 processors found frequent application in handheld remote control units for consumer electronics. That's perhaps not the most elegant application, but it does mean there are a lot of these chips out in the wild.
The specific Z8 chip I used for this board is the Z8613, which is supplied in a very interesting ceramic DIP package with an integral 24-pin DIP socket wired to the chip internally. This socket accepts a 2732 EPROM which becomes the 4KB code space for the processor. These were very expensive packages that were intended for development use. I was lucky enough to score a tube of them several years ago, brand new, on eBay.
The board contains the bare-minimum support circuitry for the processor and external RAM. All it needs is basic address decoding and latching. I used a MAX232 for RS232 level conversion, and a 6264 chip to provide 8KB of static RAM. I built it using wire-wrap techniques on a piece of pad-per-hole perfboard.
Interestingly, Zilog also produced a Forth system for this processor. It took quite a bit of digging over several years, but I finally found a copy of it as a hex dump, as a part of a very old research paper. It had deteriorated too badly to be scanned, so I ended up typing in the hex dump (4KB worth!) and burning it into an EPROM for this board. It works! Quite a miracle, actually, considering the error-prone nature of typing in that much data from a faded printout.