Sun 2018-09-09 19:19:29 -0400
I came across this really neat video, “Building a small Z80 computers – how old computers and consoles work,” where the author builds almost the simplest possible working Z80 computer. The Z80 was the processor at the heart of many of the CP/M computers in the late 70s and early 80s. The Sinclair ZX80 and ZX81 BASIC home computers also used the Z80.
The computer he builds is working but he hardwares the memory data lines to be all zeroes meaning every memory location appears to have an ASCII 00 NUL character in it. As a Z80 instruction that’s the NOP (no operation) which does nothing. So the computer runs but it doesn’t do anything. That’s still not bad for a computer that is only built with some resisters and LEDs with no logic components at all. However, he also wires LEDs to the address lines so you can see the computer counting through the addresses as it runs. He also builds a simple clock from a 555 to drive it at a very slow speed so you can see what it’s doing.
This is incredibly educational, enjoyable to watch, and you can actually follow along and do this yourself. There are Z80s available online.