Anyone recognise these custom graphics?

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Erm
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Anyone recognise these custom graphics?

Post by Erm » Fri Jun 21, 2019 1:34 pm

I bought this fantastic looking contemporary custom case-mod ZX81 on German eBay. The seller didn't really know for sure what it was but I suspected there was a ZX81 board inside, and there was (an issue 1 board with chips etc dated around week 30 of '81). Also inside was a dk'tronics 'Llamas' 4k graphic ROM, so that was a bonus. I think whoever made this must have been a serious ZX81er at the time as the graphics ROM also included an extra eprom for user defined graphics. I added a video mod, repaired a couple of non responsive keys and got the thing going. It all seems to work, including the ROM upgrade, so I have hundreds of little sprite-like things.

The first 2 pics show the x2 sets of 64 custom graphics characters (with no spaces between them). They look like they may have been intended to be some kind of textured detail or something or other that the original owner spent some time creating. Does anyone recognise what the odd patterns may have been used for? Probably just some kind of home experiment (or corruption!?).
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I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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mrtinb
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Re: Anyone recognise these custom graphics?

Post by mrtinb » Fri Jun 21, 2019 2:06 pm

Maybe the 2x 64 characters are RAM based, so it's just random garbage?
Martin
ZX81, Lambda 8300, Commodore 64, Mac G4 Cube

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Erm
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Re: Anyone recognise these custom graphics?

Post by Erm » Fri Jun 21, 2019 2:39 pm

It certainly does look quite random. I suppose I should have tried the same thing with a normal ZX81 without the extra board.

Here's the page (5) from the manual with a simple basic program to view each of the character sets.

When I enter 11944 and 11949 as the input, it displays the characters in the pictures above. But I must admit I don't really understand the technical side of all this (you may have guessed). Both the extra chips are clearly eproms and not RAM, I think.
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I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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1024MAK
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Re: Anyone recognise these custom graphics?

Post by 1024MAK » Fri Jun 21, 2019 6:40 pm

The graphics you posted don’t look like UDG data. Either the contents of the EPROM have faded away (which can happen), or that EPROM contains machine code and not UDG.

See also these threads here and here ;)

Mark

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Erm
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Re: Anyone recognise these custom graphics?

Post by Erm » Fri Jun 21, 2019 8:43 pm

The other Eprom is certainly ok, I have all of the other characters available. Love the lower case letters etc.
I'm Chris, a Brit in Germany (Chr$ on the QL forum).

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XavSnap
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Re: Anyone recognise these custom graphics?

Post by XavSnap » Sat Jun 22, 2019 2:53 am

:lol:

I think this corresponds to the location of two sticky ribbons removed.
They are placed on the bottom of the keyboard?

… anti-slip hadesif !

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