Sinclair ZX80 / ZX81 Forums

Just a thought, was the h4th ROM originally written to run on a TS1500? Only that machine has a Timex “ULA”. Mark No the original EPROM based software was originally called Multi-Forth ,then changed to Pluri-Forth, by Tree systems, Grand Rapids Michigan, for the ZX81 and TS1000. The original copyri...

This seems the most credible answer to this little puzzle, many thanks for that, Adam.

Hi Andy. The ROM can be found here... https://www.sinclairzxworld.com/viewtopic.php?f=3&t=2632&p=28741&hilit=h4th+rom+bug#p28741 The only difference between this and the bugged h4th ROM found in Eighty One(still there) is a minor correction to a maths routine, the display routine is unaltered and wi...

Minority interest I grant you but worth mentioning I feel. Those of us who use h4th may have noticed that when using an inverse screen the furthest column to the right always remains "uninverted" (see Picture). One idea put forward suggested a timing problem being that H4th seems to be a 50 hz clone...

Clever sod!!

I think most of us are familiar with BASIC games creator Andre Baune and how he manages a fair turn of speed with his creations well I thought I'd try his Alien Mind a BASIC puzzle game, with the new fast ROM, and the speed increase is fantastic.

Try it and see.

Well just had to fire up the burner and see what all the fuss was about. :lol: Having burned suitable EPROM courtesy of my Spectrum EPROM programmer I plugged in the EPROM and tried a few tests of my own. First I tried a random chaotic fraction generator of my own device which, rather than use the z...

Superb work Zsolt, time to fire up the EPROM burner!

I found with the ZX81 and a ZX8-CCB there is variance in results from one TV to the next. I have a normal resolution old LCD TV that easily produces a perfect picture, an old glass screen TV that normally does, a 37” Sony Bravia that is either perfect or awful and a small LG which is extremely pick...

There are three not two ULA types as Mark has already pointed out ULA 2C158E being the earliest. As for what's in your 81 if the board is red when viewed through the vents underneath then most probably it has the later back porch ULA 201E, if the board is green then possibly one or other of the two ...