I learned to program the Z80 microprocessor in Z80 assembly language by building a Timex/Sinclair ZX-81 kit and adding memory to it. Pictured above is a Hunter static RAM board that could store 4K of data over power cycling. I added a battery as suggested in the manual, with a switch to enable it before turning off the ZX-81.

Byte-Back M-16 16K Dynamic Ram

The ZX-81 came with a measly 2K of RAM. Even so, it was enough to write simple programs in the built-in BASIC language. For assembly language programming more RAM was needed. I built two Byte-Back M-16 memory board kits. One was more heavily modified.

The toggle switch allowed the 16K to be placed in different blocks of the 64K total memory space.

Number 1 had and extension edge connector for adding a second accessory.

After 40 years, there’s quite a bit of corrosion from the no-clean 60/40 solder I used.

The cheat sheet has memory locations used during assembly language programming.

I hear there are still computer geeks building and programing the ZX-81 microcomputer. It was a great way to learn Z80 assembly language.