ZX81 and Commodore DM 602 / Philips 802 green monitor

A composite video output comes in very handy, as it allows the ZX81 to connect to many displays that were used for other home computers of the time.

Commodore DM 602 monochrome monitor, heavily used

Having an old, battered Commodore green monitor, and a ZX81 equipped with a composite video output, the two were connected.

ZX81 to monitor composite video connection

Composite video is actually a color video signal, of which only a "low" or "high" value per pixel will be used by a monochrome monitor, loosing all precision of intermediate values that represent more colors. A "low" signal pixel will be black, and a "high" one will be white, meaning green with the Commodore DM 602 monitor. The ZX81 generates only black and white, so it's a perfect fit.

ZX81 on a green screen monitor :-)

(No) surprise: It works!

ZX81 looks (just as) great on a green screen!

This monitor might be known as:

Commodore DM 602

Philips 802

Philips BM 7500

Highscreen (model name unknown)

(Is this correct? Can you add Highscreen model name? Please leave a comment.)

"ZX81alive" removed - YouTube and the algorithm

YouTube channel "ZX81 alive" got removed by the dumb algorithm.

This phenomenon is being reported by countless, even highly successful YouTube channel owners these days: Your videos get blocked for basically nothing, and you're risking loosing your channel.

In my case, the channel was removed right away. What has happened - I think - was this: I used to have another channel, about films, that got removed, and, well, more or less rightfully so. (No copyright issue, but too much content that's already on YouTube.) I accidentally clicked on that removed channel, then switched accounts to "ZX81 alive" channel, and left a comment on a video game video. The next day, I got the message that the channel has been removed, claiming "circumvention", which apparently means using another channel to do what one used to do with a removed channel.

Which clearly wasn't the case. Or, if it was, then YouTube's "switch account" menu item is a potential kill switch. Which I'm assuming it isn't supposed to be.

Now I fear switching channels at all. What happens after I switch to - now removed - "ZX81 alive" to appeal the decision? Will the next click remove the next channel? Who knows, but the algorithm? 

It's up to me now to put in time and effort to appeal - but I don't even want to try. It's ridiculous. I don't want to support a system that's driven by a dumb algorithm. It was fun for some time, but when your channel gets removed immediately, no warning, for doing nothing bad, just because the algorithm finds a superficial pattern in user behaviour, but does not see the actual content of what has been done, then running a YouTube channel becomes just a game of luck. One click, and it might be gone.

"ZX81 alive" didn't have much content, so that loss is easily tolerable. But loosing trust and motivation isn't cool. YouTube is more and more becoming mere machinery, detached from the users that keep it alive. To some degree, this is a natural progress that goes hand in hand with the growth of the platform - but it's also quite shocking how simplistic YouTube's "safety" (?) algorithm seems to be designed. 

So, it seems that if you to run a YouTube channel, you better make sure you have a streamlined, easily approved production process, and closely stick to it. If you don't, YouTube might just erase any progress you've made so far. Which really isn't very user-friendly.

Cosmic Payback - hi-res 3D gaming on 16K ZX81!

An awesome looking hi-res 3D game for the ZX81 was just released.

"Cosmic Payback" was originally created for the ZX Spectrum, but developer John Connolly found a way to implement it on a ZX81, too. Which is quite an achievement, because "Cosmic Payback" is a 3D action-puzzle game with a bouncing ball, requiring a little bit of visual detail, meaning it would be near impossible in only 64x48 PLOTzels, let alone 32x24 characters. 

Whatever Z80 assembler code wizardry is going on only Mr. Connolly knows - but the result is nothing short of stunning. It looks like an actual 3D game, as opposed to some character-based approximation, it's reasonably fast, certainly smooth, and plays really nicely. The game has 15 levels of bouncy grid-maze action, set on a planetary surface made of different types of floor-tiles, including portals, moving ground, and more. Your goal is to collect gold - and save humanity!

"Cosmic Payback" can be freely downloaded (see link below), requires 16KB memory expansion, and supports ZXPAND joystick.

Here's a video of "Cosmic Payback" on Villordsutch's YouTube channel (2025-06-22): 

https://www.youtube.com/watch?v=W9UMdtX1U-U

Go to the game's itch.io website for more information and download:

https://connosoft.itch.io/cosmic-payback-zx81

Also check out the ConnoSoft's other projects at:

https://connosoft.itch.io 

https://www.connosoft.com

Game: Tai (1982)

Can you defend Tai against the Imperial Forces?

"Tai" has some great cover artwork that suggests something along the lines of the "Star Wars" and "Dune" movies, somehow esoteric, and maybe a hint of much later 16-bit game "Syndicate", or something. But most of that is just make believe - the cover is still great, it gives a nice visual context to the game's storyline, but there are no characters or people in the game, and it has no strategy elements. "Tai" is a vertically scrolling & 3rd-person-view fake-3D shoot-em-up game. 

"Tai" (1982) gameplay, first stage: straightforward & fun

The first, vertically scrolling stage looks good, but isn't that spectacular. Controls are straightforward, and after a couple of attempts you'll probably be able to make it through. It works well and is fun to play - but it's only the build-up. The real challenge is the second stage. It's a 3D-like view of a Star Wars "Millenium Falcon" style spaceship which is being attacked by TIE fighter like enemy ships. The action gets a little chaotic, with your gun firing in several directions, and the enemy ships moving around quickly, but it looks fantastic, and there is a bit of an actual 3D feel.

"Tai" (1982) gameplay, second stage: (almost) 3D open space battle!

Overall, "Tai" is a very good job. Some obvious effort went into the stage design - visually, it's among the best charset-based ZX81 games. The fact that stage one and two are two distinct game modes gives it indeed some epic proportions. The first stage would've benefited from some sort of extra feature, but trying to make it to the second is all worth it. And it's quite difficult to finish, so it'll keep you occupied for a long time.

Rating: Make sure you make it to the second stage! 7.5 / 10

"Tai" (1982) Cover artwork

If you'd like to try "Tai" yourself, here are possible sources: 

https://www.zx81stuff.org.uk/zx81/tape/Tai

https://spectrumcomputing.co.uk/entry/29364/ZX81/Tai

The Timex Sinclair User's Encyclopedia, 1984 (book)

Very nice book! Maybe a bit more for the beginner, or generalist, but also the experienced user and specialist will find tons of interesting information in it.

"The Timex Sinclair User's Encyclopedia" by Gary Phillips and James C. March is a huge, extended glossary of pretty much everything you can think of regarding the Sinclair ZX81, Timex Sinclair 1000, and Timex Sinclair 2068. It covers manufacturers, peripherals, hardware components, software titles, BASIC keywords, algorithms, binary logic, IT terminology, abbreviations, and what not else, each with at least fundamental information, and in most cases with some extra bits, like some example code, or further keywords. With more than 200 pages, it really has a lot of content. If you're looking for something ZX81 (up to 1984, and a little beyond), you'll definitely find it in this book. And if you don't, you can still easily spend many hours browsing through the pages.

You can get it from archive.org:

https://archive.org/details/the-timex-sinclair-users-encyclopedia/

The Timex Sinclair User's Encyclopedia (1984) book cover

 

Game: City Patrol (1982)

They're coming! You are in command of a laser-gun equipped ship - destroy as many alien suicide ships as possible!

In the early days, computer games didn't need over-elaborate backstories. Computer means space, space means aliens, aliens means destruction - there you go. "City Patrol", released in 1982, has a simple concept, and is a very exciting game. A stunning graphics engine, and versatile controls, make it one of the best action games for the ZX81.

"City Patrol" title screen

In a side-scrolling view, your goal is to protect the city and its inhabitants from destruction by alien invaders. In order to do so, you guide your ship along the city, trying to hit an alien invader with your laser beam. If you can't get the invading ship in time, he (or whatever "it" is) will reduce part of your city to rubble. But be careful, not only will the invader harm your city's buildings, but your laser will do so, too, in case you miss.

Credits/info screen

"City Patrol" uses an interesting input scheme: Only four keys are required to steer your ship up and down, left and right, set speed low or high, and fire your laser. The trick is: Hold "left" to move left slowly, then press "right" to speed up, and vice versa. Hold "up", then press "down", or vice versa, to fire. (The actual keys are F, V, J, and N.) Additionally, any other key will trigger your laser cannon, too. (Except A, which is used to quit.) That's a bit unusual, but after some practice, becomes intuitive and turns out to work very well.

The full screen, multi layered, side-scrolling game screen...

The graphics are, of course, blocky and crude, just like pretty much all ZX81 graphics. But, as you can see in the screenshots, the ZX81's character set is well suited to simulate buildings in a nice metropolitan "skyline" view. The overall dark appearance gives is a dystopian undertone, which matches the game's idea perfectly, and - a rare occurrence among ZX81 games - even the cover artwork (see end of article) to some degree. When motion is added, the effect is quite spectacular. Programmer Don Priestley managed to create four layers of overlapping full screen parallax scrolling (!), and "City Patrol" redraws these at full frame rate.

Add to that the clever controls with possible high speed movement, big flashes on screen (*light epilepsy warning*), and challenging gameplay, and you get a surprisingly convincing, visceral experience.

...is quite stunning, esp. when in fast motion.

On first sight, "City Patrol" is simple, wild, and a bit confusing. There is a bit of a learning curve. Once you get it, it becomes frenetic and addictive, while still being difficult enough to keep you occupied for a long time. With a little suspension of disbelief, yeah, it really feels like flying along skyscrapers, hunting aliens, and saving people!

Rating: 

It's a bit low on features, but for what it is, it's massive.  

8/10

"City Patrol" (1982) cover artwork

If you'd like to try "City Patrol" yourself, here are possible sources:

http://www.zx81stuff.org.uk/zx81/tape/CityPatrol

https://spectrumcomputing.co.uk/entry/28760/ZX81/City_Patrol

DevLog001: Parallax scrolling in a game

My attempts at horizontal parallax scrolling turned out to be somehow usable - so why not create a game?

After some experimentation with BASIC, strings, MCODER2, and z88dk, and having some experience with C code, I began rewriting my efforts, gradually adding game-like functionality. So far things went along nicely, the code generated by z88dk doesn't seem to be as efficient as that generated by MCODER2, but good enough to create some fast loops, esp. for graphics. The huge advantage of z88dk and C code is its usability - meaning you're using ASCII text files in a Linux environment, with all its proven tools like vim editor, git version management, diff, make, networking, etc., and you have all the power of a C compiler, meaning #define, functions, labels, pointers, types, etc., to write proper code. Of course some extra work is required to transfer the results of a Linux cross-compiled C program to your real ZX81 machine - but during development, using an emulator, the workflow and turnaround-times are amazingly smooth and quick.

A title screen with instructions / info

Creating graphics on a ZX81 is always a bit of a peculiar challenge, unless you're a very experienced machine code wizard, able to use hi-res graphics. The fixed character set doesn't give you much to work with, but when time and motion is added, the illusion of a "big" arcade game is actually quite enjoyable. 

So currently this little shoot-em-up game-thing is called "Nemezys 2081", has pretty much the parallax scrolling as shown in the BASIC/MCODER2 tech demo videos, and you can actually do something with it: move around and shoot a bullet! :-)

Game screen: ship, enemy, bullet - it's a shoot'em-up!

I have a ton of ideas that I'd like to put into the game, but I also have zero idea if it'll work out. A C compiler potentially generates more code than strictly necessary, and CPU cycles are tight on a ZX81. But it's great to just add features and see the progress, even if memory runs out, or it becomes just too slow - it's a fun learning experience, thus a win-win situation in any case. 

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Thanks for reading, see ya next time!