Its been a while since I wrote something for this blog, mainly due to pressures of work. However its summer now and I’ve managed to carve out some time to do other work related projects. One thing I’ve done in one of my undergraduate classes is host an honors projects which students can opt into. Part of this is to prove to me they can soldering electronic components onto a PCB board. Every engineer should be able to build electronic gadgets from scratch and solder is an essential skill to have.
In order to keep myself in hardware practice this summer I decided to go back in time and search out a Z80 microprocessor kit to build. When I was a teenager I built and designed my own Z80 system. If I remember right it had 512 bytes of RAM, switches and LED lights to enter and run programs. Once the machine was switched off however it forget any program that had been entered. I’d planned to add a hex keyboard etc but my money and spare time ran out. If you search the web you’ll find many Z80 based projects in various degrees of sophistication. There is an entire community of Z80 builders. Some specific ones that caught me eye include:
Those too young to know what a Z80 is, its one of the early microprocessors that came out in the 1970s, 1976 to be specific. It was basically an enhanced version of the 8080 a very early and popular Intel microprocessor. What was key about the Z80 was that is was quite easy to construct a basic computer using the Z80 chip. The chip required very few support chips, for example the clock was a simple single-phase clock (easily made from two NAND or NOT gates) and it only required a single 5v power supply. These and other features made the Z80 a very popular microprocessor at that time. Many famous and not so famous pre-IBM PC computers were build using the Z80, including the TRS-80, Nascom 1 and 2 (I had the Nascom 2), the famous Sinclair ZX80, ZX80 and ZX Spectrum, Amstrad CPC, Jupiter Ace, and many others. You can still purchase the chip new for only a few dollars.
My problem is I don’t have the time to design a new system for myself so instead, I hunted out any available kits. I found one and a nice one at that called the CPUville Z80 computer kit. This kit was developed and is sold by Donn Stewart. He has various addons to the base CPU board such as a serial interface and disk and memory expansion. What is also nice is that he adds the facility to single clock the microprocessor at very low speeds so that one can observe the operation of the computer in detail. Given my birthday is in July I decide to order one of his kits for myself. His kits are very modestly priced, the basic CPU board (I fully working Z80 computer) only costs $42 dollars. The kit comes fully complete except for the 5v power supply, but Donn can also supply this. The computer has 2K of RAM and a preprogrammed 2K ROM with various test routines included. Data is entered through a bank of 16 switches and output is via a set of 16 LEDs. To program this computer you’ll need to know binary and hex, and no you can’t browse the net using this computer.
Having obtained the kit, I assembled the various components. The kits comes with an excellent assembly and operation manual. The kits itself only supplies a few chip sockets for the CPU, RAM and ROM. I tend to be more cautious so I purchased a bunch of 20, 8 and 7 pin chip sockets. It probably took me about 6 hours to build. The board has about 500 soldered connections so you have to take your time and check the quality of your work. I took some pictures of the board during construction and a video to show the computer working. Amazingly it worked first time. Operation involves flipping a switch to halt the CPU, entering an address in ROM where a test program is lcoated and then releasing the CPU to run. The test program I ran was a simple counter than counted from zero to 65536 and output the binary number to the LED lights. If you need some fun with a very basic computer this seems to be the one to get.