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I am building a Z80 computer

May 20, 2013

I am building a Z80 computer, based on the Zilog Z80 Z84C0006, a 6MHz CMOS version. bdk6 has started a very similar project at nearly the same time, We will certainly exchange ideas along the way. Other than bdk6 I will build a modular system with several extension boards, and my version will probably run Microsoft BASIC later. Much later...

As I have never built a Z80 computer before I will start with a bare minimum version, devided in 3 mile stones respectively boards:

Board one (200 x 150 mm perfboard) will carry the CPU, the ROM (EEPROM), oscillator(s), reset, PIO and power supply circuitry. There is enough place left to add serial access, RAM and other fancy stuff later.

Board two (150 x 100 mm perfboard) will carry 7-segment displays with according drivers and control circuitry to display current data and address bus status.

Board three  will be a kind of homebrew Arduino shield EEPROM programmer (I am too lazy to move a lot of DIP SPST switches).

Next steps will be to draw the schematics of each board and gather parts.


May 23, 2013

I managed to finish the bare bone version schematic of the Z80 computer for first experiments. I mainly followed the instructions and explanations on The First Great Z80 Project, beside studying all the data sheets. The computer is in the moment just clocked by a 1 Hz Schmitt trigger inverter oscillator, later it will be clocked by a 6.144 MHz OSC.

The next step was to make a kind of wiring plan for the address and data bus. You can find the wiring plan in the attachments. As I have no wire wrap equipment and I am not a fan of cable spaghetti, I desided to put the address and data bus wires on the top side of the board. The chips and wires are aligned at a grid of 2.54mm. I have also included the RAM already on my wiring plan; I will just leave the IC socket blank in the moment. The connection dots in the wiring plan are actually single male pin headers, so it's easy to connect several wires on one spot and have access to every address and data line with a logic probe etc. This makes the board bigger than it must be, but it hopefully helps to keep track and I can later route a PCB if this ever goes beyond experiment and prototype status.

Bare_minimum_Z80_computer.JPG456.73 KB
Address_and_data_bus_wiring_plan.JPG171.48 KB

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Let me know if you're looking for parts from that era. I have some Timex / Sinclair ZX81's and some of the memory & interface chips.

I even had an S-100 buss computer built around the Z80. Don't know if I still have it, may not have survived the last purging of my shop.

With recent life events, (unemployed, and scrapping a LOT of my old scavenged equipment), I've begun thinking of wiring-up something based on a Z80..  Most of my robots, have been either Parallax BS2 or Arduino based, but I've been thinking of building a controller to both handle output to the arduinos, and connect to the outside world, back to a PC using simple 433Mhz 2-way digital modems. (Parallax parts)..  I only wish I could remember, what i did 20 years or so ago.. I used to cut my teeth writing 8080/85 assembly, for either an old TRS-80 Model-100, or an Osborne-1 computer...  Now, I've recently inherited (Okay, Rescued from the scrap heap) 8080 computer trainer.. (already been in contact with someone who still has the manuals, but he doesn't want to part with them.) ..  I've seen someone out on the net has a full operating Z80 based computer using only 9 chips.. I've run across several other plans, schematics and even a bare metal source for CP/M 2.2, but I still can't quite remember my old hard-hacking days...  Not giving up though!  Stephen Griswold