ZX80 Core - new ZX80 motherboards

[PokeMon]

For the 27C512 to work you have to also disconnect the WR signal by removing R97, otherwise it pulls it up to 1 always.

Okay - I see, I have to update the ROM switch setting for it.
So the pages with A14 low are not allowed when using EPROMs of type 27C256 and 27C512.

Anyway there could be used 32 kByte with EPROM either.

It is not my work, NOSTALCOMP http://www.nostalcomp.cz did it. It is really nice and comfortable to have Renum by hand in BASIC and also to be able to run all BIG ZX80 games simple and quick for anyone to show the ZX80 capabilities.

I will also post on my blog soon a new ROM contect for testing RAM from another friend of mine - Louis Seidelmann. It is most useful for old ZX80s and ZX81s with RAM packs, but you can use it with ZX80 replica or ZX80 Core too to check that everything is as it should be. It is simple 2kB ROM replacement which tests 1-16 kB of RAM using two differnet algorithms, showing errors and problematic bits. Everyhting in nice user interface.

This is interesting for me, too. For another project.
I worry to be very busy next time.

[PokeMon]

So here is the workaround for the pulldown resistor for pin 1 of EEPROM 28C256.
Right hand of R96 (bottom view) there is a big copper area with GND.
It is the easiest way to solder a SMD resistor here and to scrape the white paint before in size of the resistor.
I would prefer 10k but any value from 3k3 up to 100k would do.

EEPROMpatchsk.jpg (150.59 KiB) Viewed 4122 times

[Kiwisek]

This is a good idea. I put it on the top of the board on mine ZX80 CORE. One pin to the hole for unused R31 and the other one to the R96.


The othe 10k pulldown I put on the bottom between pin 27 of EPROM and the upper pin of C7.

[PokeMon]

Yes, looks good as well. As for the other resistor you need the pulldown resistor at pin 27 but you have to remove the resistor R97 as well and do not have any more the chance to use an EEPROM with write option. So I decided to change the documentation for pages useable for 27C256 and 27C512. So 27C256 does not give more address space than the 27C128. 27C512 gives 32 kB of ROM without changes on the board. So I will let this as official but people are free to change as desired as well.

So I uploaded the updated documentation which can be found here:
http://www.8bit-wiki.de/index.php?id=3& ... 7ad2d90000

[retrolab]

Hello.

What about the zx80 compatible cases?

[PokeMon]

I don't know. Do you have some ?
The board is compatible to the original ZX80 case.
I plan to do a transparent case for it but not now, maybe next month.
So I had some more time in the summer holiday but now I have some normal work as well and there are some other extensions to develop.

[retrolab]

Hello.
I would like to try to make a new one but I haven't an original ZX80 to obtain the measures. Anyone knows its measurements (width, height, depth)?
Thanks.

[PokeMon]

You can try to contact Markus_8008 on the german board in this thread:
http://forum.tlienhard.com/phpBB3/viewt ... 2&start=75

He works on a 100% copy of that case and has construction data as well. I think he did a try on Shapeways with a 3D printer but I don't know if he is convinced from the quality - not sure. Try to contact him.

[PokeMon]

Today I had a problem when testing another ZX80CORE board.

The cursor "K" appeared but no reaction on any keypress. After measuring the keyboard I found a short which has been made during production of the boards when coating them with tin (HAL). So maybe the very short distance in the key loops on the PCB could cause an error. See the picture I made:

IMG_6713sk.JPG (147.8 KiB) Viewed 4006 times

Another guy from the german forum had a similar problem. So it is recommendable to check the keyboard function first before soldering SMD tactile switches or mounting the keyboard membrane. This can be done simply with a short wire with a bit removal of plastic of the end and tipping on the "keys".
In my eyes the distance is not too short with 12mil / 0,3mm between these small wires but maybe more distance is needed for areas with partly missing stop mask.

I will add this information in the manual soon.

[PokeMon]

The illumination kit is ready now.
The idea was born as somebody on the german forum asked for a power LED. So I thought about something special.

There are 2 multi color LEDs used that are wired in series and supplied with the unregulated 9-12 Volt from power supply. These LEDs are controlled via 3 internal signals of the ZX80CORE and illuminate the board in different colors, depending on the CPU activity. There can be made more mixed colors and brightness controlled via a specific programming and influencing the signals for activity. The LEDs have been angled of about 90° to use the white color of the board as reflection area.

More conservative people may use one or two simple LEDs as well if you find it to modern. I will provide more information of simple Power LEDs soon. But I find this IKIT quite cool.

MulColLED1k.jpg (130.53 KiB) Viewed 3983 times

MulColLED3k.jpg (137.08 KiB) Viewed 3983 times