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Sinclair ZX80

The ZX80 was released in 1980. Here for the first time was a simple and most important of all affordable personal computer that anyone could buy and use. Granted, the 1K of RAM limited what one could do straight out of the box, but with an optional RAM expansion unit of 16K fitted the little machine became quite capable.

Modern Replica and Software Programs

Here is a .zip file containing a variety of games and .O/.P conversion utilities I collected from all over the Internet. The .zip file contain games for 1K, 3K and 16K RAM configurations. All rights belong to the original content creators. The files are merely mirrored here for convenience and no copyright infringement is intended.

Grant Searle produced a gorgeous and extremely accurate replica of the ZX80. It is an impressive feat of reverse engineering. Visit his site for more information. I have managed to purchase a ZX80 replica kit. The board and keyboard quality is top notch! Some of the components provided were incorrect though. A 5.5MHz resonator was provided instead of a 6.5MHz one. Also missing was a 74LS04. Instead, the kit provided a 74LS08 which is wrong. One or two incorrect resistor values were also provided. Check the ZX80 schematic and board photo below during building to confirm component values and placement. NOTE, Grant is not involved in the production of these kits.

Here is the link to the 74LS74 based BACK PORCH TV SIGNAL GENERATOR I tried. This one is fully reversible. This site shows a very well designed back porch generator using a 555. The designer also provides a link to an excellent description of the circuit's operation.

This back porch generator works extremely well and produces a crisp, bright picture! The transistors can be substituted with BC550.

Picture from ZX80 on monitor using the 555 based back porch circuit below.

Unbuilt kit

Some components provided were incorrect, but the quality of the board and keyboard is excellent.

Placing Chip Sockets

The pads are tiny so use plenty of liquid flux. It helps a great deal.

Placing Chip Sockets

Chip socket placement completed. The one RAM socket is the wrong way round. (doh!)

First results on screen

Running with no back porch and 6MHz crystal instead of 6.5536MHz crystal, so video quality is still poor

Completed

The keyboard membrane has a small bump on each key and simply sticks to the PCB.

Detail of chips

One or two equivalents used but overall everything works.

Back Porch Circuit

The 74LS74 based back porch circuit is shown. Poor performance! Link in the text

No Back Porch

The video output has no back porch typical of a stock ZX80

Back Porch Added

The newly introduced back porch can be seen in the video signal using 74LS74 based circuit. Allthough the back porch is present, video quality remained poor.

Video with back porch

Some improvement using 74LS74 based circuit. Not quite as much as I expected.

Without back porch

Dark video, but my monitor seems to still handle it well.

ZX80 Schematic

The schematic for the ZX80 that'll make it possible to find the VIDEO and SYNC signals for the back porch generator.

Complete board

Top right is the game controller. This is hardwired to the cursor keys. Bottom left is the 16K RAM pack.

Closeup View

To the left is the back porch generator

Front View

Gaming

Running ZX80 KONG

Kempston Interface

Compatible with ZX Spectrum, ZX81 and ZX80

Kempston Controller Interface

The Kempston compatible joystick I constructed. The newly constructed RAM pack is to the right and interfaces with the joystick controller.

Game Pad

With Up, Down,Left, Right and Fire buttons

Back Porch Generator

Now powered from its' own supply.

Complete Setup

Ready for Pacman or KONG

Inside the original ZX80, (right-click and open image in new tab for more detail) Grant Searle

 

People still produce software for the ZX80 and there are some excellent games out there.

It is possible to turn a ZX80 into a fully compatible ZX81 by upgrading the ROM to 8K BASIC and adding a small amount of additional circuitry to handle the generation of the display while the CPU is busy. It is also necessary to use a ZX81 keyboard overlay since the keyboard mapping is different to a ZX80. This will allow a ZX80 to function as a ZX81 supporting both slow and fast modes. The additional circuitry is called an NMI generator. Visit Grant's excellent site showing his NMI generator design as well as Martin's site showing his design for an NMI generator PCB. A ZX80 replacement ROM with 8K BASIC is available from here. Ask the seller to program the ROM with the appropriate ROM image.