Grant Searle’s z80 Computer

If you’ve searched any portion of the internet for the terms “homemade” and “z80”, there is a high probability that you’ve run across Grant’s Page.  Grant’s work is essentially the Holy Grail for the beginner.  He gives you the tools you need to have in order to understand how to build a generic z80 circuit.  As well as well documented software which can be modified fairly easily.

Grants circuit gives you a very basic (pun intended) serial based computer running Microsoft Basic 4.7b (a variant actually written by another individual who’s name escapes my memory at the moment).  The computer’s I/O is interrupt driven by the 6850 UART, and has enough leftover space in the ROM to place a monitor or any other code that you’d like to use.  The computer’s original speed is 7.3728mhz.  However, the example above has been modified to use a 1.8432mhz oscillator.

Even regulated down to a quarter of the speed of the original, this computer is more than capable of handling most basic programs.  And with 32kb of RAM, you’ll likely not find yourself running out of program space.  And programs can easily be transfer from a PC to the computer by simply typing the programs into a text file and then copying and pasting them into your terminal program.

Added breakout pins around the z80 on my personal computer allow me to prototype circuits and test them with the IN/OUT commands in basic.  A handy feature indeed.

If you’re looking for a simple circuit to build, and you’d like to have your own homemade z80 computer. Might I suggest that you head over to Grant’s website, and give one of his examples a try.

TEASER:  There will likely be another z80 Computer article coming in the following days.  Not to give too much away, but it DOES NOT involve a homemade example.  I’m working out a deal to acquire something special.  I’ll know the full scoop within the next 24 hours.  Until more is known, we will be referring to this as “Operation Speed Racer.”  I’ll let your mind go crazy now…

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