Post

@breakintoprogram.co.uk

I wrote yesterday that the ZX81 has a native graphics resolution of 64x48. That's not strictly true. It has a pixel resolution of 256x192, but has a character map of 32x24. The PLOT routines use the graphics block characters as pseudo-pixels to effect a resolution of 64x48.

9/9/26, 8:14 am2 reposts23 likes

L Break Into Program

@breakintoprogram.co.uk

9 Sept

To confuse matters more, there are a handful of techniques to force it to do hires graphics, and there are a handful of games that do just that, including an incredible port of Manic Miner.

youtube.comManic Miner on the ZX81 in High Resolution - Unbelievable but trueYouTube video by Villordsutch

L Break Into Program

@breakintoprogram.co.uk

9 Sept

Oh and the character map, also known as D_FILE. You'd think that this is a 32x24 array in a static position in the memory map. Ha! Gotcha!!

zx81keyboardadventure.comPeeking into the ZX81s Screen MazeRetro computer blogging on games, software, electronics, Arduino, Raspberry PI & projects for the Sinclair ZX81, ZX Spectrum & retro other computers.

L Break Into Program

@breakintoprogram.co.uk

9 Sept

And how it generates the video is also incredibly bonkers and very Sinclair.

blog.tynemouthsoftware.co.ukHow the ZX81 Generates VideoNow the Minstrel kits are back in stock, it's time for the second in this series of posts from my Patreon, this one covering the video outpu...

L Break Into Program

@breakintoprogram.co.uk

9 Sept

Why did they go to such lengths? For one, it inherited it from the ZX80. Secondly, you can shrink the D_FILE for systems with less than 4K; each line is effectively a newline terminated string (byte value 118). So an empty display takes up just 25 bytes, not 768. It expands each line as required.

Sharpworks

@sharpworks.bsky.social

9 Sept

Well, that's different!

L Break Into Program

@breakintoprogram.co.uk

9 Sept

Yes. It kind of makes sense though. Classic Sinclair ingenuity.