Displaying old computers on new TVs

[angus]

Cool, it's coming from Hong Kong so could take a couple of weeks but I've ordered via eBay from Hong Kong sellers before and always had the goods arrive safely.

Its good that you have an alternative use for the box, I would only really want to use one for my Zeddies and possibly the C64 that is gathering dust in the attic.

As an update, I tried the modded Zeddy on a 2004 vintage CRT television with front composite input. It wasn't a great success. If the screen is full, the display is good...but a partially full screen is very distorted. Oddly enough everything is fine for 1 second then it becomes distorted.

Tried the modded Zeddy on a handheld LCD television (from the 90's or early 2000's) and it won't work...but the unmodded one works fine via RF with the same TV.

So I am very much having partial success, with modded and unmodded Zeddy. It does seem that how modern televisions handle the signal varies tremendously between different units.

[Slipstreem]

@ angus: I'm moving home in a few days time and it looks as though I may be without Internet access for up to five weeks. It's a long story I won't bore you with, but it will most likely delay me posting here about the performance of the converter which I'm expecting to arrive between now and then. I just thought it polite to let you know that I haven't forgotten and I'll post an update ASAP.

[angus]

Thanks for letting me (and anyone else following the thread) know. Good luck with the move, I don't envy you it's a horrid stressful thing to do.

[Slipstreem]

Well, the move went fine and the magic box arrived from China only a week or so after my last post surprisingly. It works very well displaying on my 21.5" Benq PC monitor and on my 32" AOC LCD TV, both via their VGA inputs. My ZX81 is modified with just the single transistor and single resistor mod to provide composite video output and the image is perfectly stable and as clean as can be expected.

I'm still very busy with decorating right now, but the plan is to investigate mounting the PCB from this device inside the original ZX81 case to provide a direct VGA output. Whether there'll be enough space for it with the planned internal 3.5" LCD screen or not remains to be seen, but I'll certainly have a go if it's at all possible.

I still haven't finished unpacking yet and have no idea where my digital camera is at the moment, but I'll post a screenshot at some stage if anyone's interested.

[Moggy]

Hi Slipstreem.
Look forward to the pics , an interesting project

Regards
Moggy

[PokeMon]

Hi there,

I wanted to let you know that I am working on a USB interface for ZX81 to transport video signal in a MS window on the pc. Maybe transport of data as well but I thought of this device for crystal clear video signal in a scalable window (256 x 192 or greater).

[sirmorris]

Hi PokeMon, Welcome aboard!

That's an interesting idea - is there anywhere we can see more details??

C

[PokeMon]

Not yet.
I am working on it and maybe in about 3 or 4 weeks I know more about.

It will be realized with Maxims MAX3420 USB Peripheral Controller Chip and main purpose is to transport video to my computer to work with.
But when the USB interface is realized its not to hard to transfer data. So this would be next step and also adapting the tape interface to load/save data from PC.
I have several ideas for expanding this solutions and could have some really nice features using a physically ZX81 - not any emulator. That's the goal.

Unfortunately you have to adapt three signals directly from ULA, video/tape out, 6,5 MHz clock and tape in. This is the only but must modification to use this feature which will give much more benefit. I will do it with a 4-pin audio/video jack 3,5mm which is fixed to the case, three few inch cables, three resistors (to protect ULA against shortcut) - thats it. No other modifications - especially not to original ROM image.

So I hope to report more in a few weeks in this "theatre".


Maybe someone can help answering some questions about physical memory layout of the good old zeddy.
As I found on the internet you could be the right person to answer this.

Standard is
0-1fff system ROM
2000-3fff unused space ?
4000-7fff 16 k RAM (extension)
8000-ffff probably not used

I know there could be several modifications. I can not keep in mind all solutions ever made but maybe the main existing solutions out there. I am talking mainly about ZX81 original hardware, no self projects like ZX96, ZX2000 or something like that. I heard that ZX printer has an additional ROM. Do you know in which address area ? Also I heard about 32k RAM modules and 48k RAM modules. Can these RAM modules simply adapted via ZX81 backplane or are some HW modifications necessary ? Which memory area use the 32k RAM ? 2000-9fff ? or 4000-cfff ? I think 48k use 2000-ffff.

Is it possible (and practiced) to run programs above 7fff ? Or is memory above 7fff is used only for R/W memory ? I think it could give problems to execute code in this area due to working ULA. Maybe this area could be used in fast mode for programs but I am not sure about this. Are there real programs greater 16k ? Maybe not many. Or is this used mainly for HIRES graphic or something else ?

Cheers, Karl

[siggi]

Maybe someone can help answering some questions about physical memory layout of the good old zeddy.
As I found on the internet you could be the right person to answer this.

Standard is
0-1fff system ROM
2000-3fff unused space ?
4000-7fff 16 k RAM (extension)
8000-ffff probably not used

Hi Karl
maybe that will help?

http://nocash.emubase.de/zxdocs.htm

Siggi

[sirmorris]

Hi PokeMon,

Siggi is right - that is one of the most definitive documents available.

C