ZX81 rebuild

[1024MAK]

Forth up and running.

May your programs go forth and multiply

Mark

[Moggy]

Splendid now enter the following.....

: lardo 10000 0 do ." lardo is a genius " loop ;

To run type lardo then enter.

[Lardo Boffin]

Splendid now enter the following.....

: lardo 10000 0 do ." lardo is a genius " loop ;

To run type lardo then enter.

Took me a while to get the spacing right...

[Lardo Boffin]

Of course had I known this bad boy (the family zeddy I thought lost) was in my folk’s loft I would have never built it!

[Moggy]

@Lardo

Small favour to ask Lardo. could you run program again but before entering "lardo" first enter CO REV which should turn the display inverse.
The reason I ask is that the original ROM code has a display bug which leaves the furthest right hand column only half inverted making the characters in that column look ridiculous.

Andy Rea's new ULA magically cures this problem (neither of us know why) and I was just curious if the new style ULA you have fitted did the same?

[Lardo Boffin]

@Lardo

Small favour to ask Lardo. could you run program again but before entering "lardo" first enter CO REV which should turn the display inverse.
The reason I ask is that the original ROM code has a display bug which leaves the furthest right hand column only half inverted making the characters in that column look ridiculous.

Andy Rea's new ULA magically cures this problem (neither of us know why) and I was just curious if the new style ULA you have fitted did the same?

More magic!!!

[Moggy]

Many thanks for that Lardo.

This is what it rectifies..

[Lardo Boffin]

Thats awesome! I suspect there is a thread somewhere but why is the screen so badly offset in this ROM?

[Moggy]

Thats awesome! I suspect there is a thread somewhere but why is the screen so badly offset in this ROM?

Adam(nollkolltroll) explained the inverse thing thus in a post...........

QUOTE.

"I've seen this when using the ROM display driver and printing 34 characters without an ending halt-character. To my understanding, this is unfortunately the behaviour of the original ULA hw that somehow ignores the invert-bit after only 2 pixels."


As for the offset you have to remember that h4th is a clone of Bob Alsum's Pluri-Forth for US NTSC and when using the NTSC version the offset is not so pronounced I believe so maybe Skywave took it as is without much alteration for PAL displays ,although they managed to introduce a maths error not found in the US original. I also recall that a forum member tried rewriting the display routine which I burnt to a succession of EPROMS but to no avail so perhaps it was easier to live with the crappy display back then.

A not so clear picture of the original US setup taken from Sync magazine .


Original article can be found here.. plus another article concerning Pluri-Forth..


https://archive.org/stream/SyncVolume4N ... 9/mode/2up

https://archive.org/stream/SynchroSette ... 9/mode/2up

[kpalser]

I’ve been trying to contact David Husband to ask permission to use the Forth ROM in my emulator. I’m no longer sure who I should be asking. I’ve read the other threads in this group and the above replies regarding the offsets.

The fact that David / Skywave Software would have gone on to write Forth ROMs for the BBC micro and CPC without being challenged by the copyright seems odd.

But then on the other hand you have Bob Alsum / Tree Systems with his Pluri-Forth ROM, where he has in the past released the source code: https://www.timexsinclair.com/?s=Bob+Alsum and the ROM screen offsets seem better suited to NTSC.

Maybe one was licensed to the other. I’m going to try and contact both authors with the key aim to get permission to include the ROM but maybe also determine who did what.

Regarding the ROMs themselves there seems to have been suggestions that they may have been modified for EightyOne. But identical files are found in the beta distributions of Xtender 2 with file dates a good 5 years before the version history of Eightyone.