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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 quality is top notch! The kits are not produced by Grant.

The link for the BACK PORCH TV SIGNAL GENERATOR I tried. This one is based on a 74LS74 and is fully reversible. Grant also has another variation as part of his NMI generator that uses a 74LS08.

Unbuilt kit

Some components provided were incorrect, a 5.5MHz resonator instead of a 6.5MHz one. Missing 74LS04, was instead provided with a 74LS08 which is wrong. One or two incorrect resistor values. Check with schematic before building.

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!)

Early results on screen

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

Completed

The keyboard membrane sticks to the top of the PCB. The quality is excellent.

Detail of chips

One or two equivalents used but overall everything works.

Back Porch Circuit

The 74LS74 based back porch circuit is shown. 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.

Video with back porch

Some improvement. Not quite as much as I expected.

Without back porch

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

Another Back Porch Generator

This circuit is by Louis Scully and makes part of his Minstrel ZX80 clone.

ZX80 Schematic

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

Inside the original ZX80 (right-click and open image in new tab for more detail) Copyright 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. 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.