ZX80 Core - new ZX80 motherboards

[retrolab]

Thank you very much, PokeMon. I have seen that with the additional module, quality is better.

[gozzo]

What we now need is some new reproduction boards of the Microdigital TK85, for those that don't know, it's an improved ZX81 with 16k ram built in (uses 8 of those nasty 4116's..BUT has 'option links' to use 4164's instead - maybe even possible to alter it for higher than 16k!), a zon-x81 compatible sound circuit(optional, some may have it fitted already, mine hasn't - yet!), entirely discrete logic - no horrid ULA, in a spectrum-type case!! Unfortunately doesn't seem to be any PCB pattern files on the net at the moment, probably the only way to get them would be to desolder all the components off one of the boards and scan it.??! (no, I'm not destroying mine - I only have one and it cost me over £100 to get it!)

[PokeMon]

What about the TK85 ROM ?
Is it compatible to the ZX80/81 ?
Does it have a SLOW mode with NMIs ?

[gozzo]

Virtually identical, functionally, to a ZX81 with 16k, but it has an extra 2k EPROM, supposedly for fast tape save/load,and maybe other things - the instructions I have are in Portuguese, which I do not understand! the sound chip (AY-3-8912) uses the same I/O ports as the zon-x81 unit,(there was instructions on the net on how to add the sound facility for TK's that don't have it already fitted - the holes in the PCB are there, just need the parts fitting in) and yes, it still has the usual FAST and SLOW modes. It's more closely a 'clone' of the TS1500, in appearance terms, although the case is thicker/higher than a TS1500 or a spectrum. As for if the main ROM is the same, I'm not 100% sure but I suppose there may be a few differences due to the extra capabilities..? The PCB is the same size and shape as a spectrum.

[1024MAK]

My ZX80CORE PCBs and parts that I ordered from PokeMon arrived today

It all looks good

Thank you Karl

Mark

[PokeMon]

Okay - I hope to maybe see a picture from some ZX80CORE systems build up in the future.

[jclt]

Of course I will do in a few days.
I want let the chance to fill the pre-oders first.

Hi PokeMon,
I'm interested in 1 motherboard.
Thank you.

[Kiwisek]

I managed to build the ZX80 Core this weekend. It is nice machine and works perfect. Thank you PokeMon! Great work!

You can find photos at http://www.8bity.cz/2013/dalsi-klon-sin ... zx80-core/. There is actually also some text but sorry for the language. You can try translate in upper right corner, but it is google and it is as it is.

During the build I found minor problems which should be noted:
- I had to add 10k pull-down to pin 1 of EPROM socket to get EEPROM 28C256 to work. It is just connected to +5V by the bank switch and without the connection it is in the air.
- I had to remove R97 and connect pin27 of EPROM to the GND by another 10k pull-down. By this change I loose in system WRITE capabilities for EEPROM 28C256, but I am able to use bigger EPROM 27C512. Without this change is A14 of 27C512 always HIGH (unless you try to write to it )
- I have a great content prepared by NOSTALCOMP http://www.nostalcomp.cz/zx80_soft.php which allows to fill 4x16 kB with ZX80 and ZX81 ROMs together with games such as Space Invaders, Breakout, Pacman nebo Kong and utilities such as RAMsize, Renum or Curline. All by hand just by entering PRINT USR(8200) or similar CALL.

I did not try the ZXpand yet.

I am looking for the instruction for the ZX80 Illumination Kit and for the NMI Generator.

[PokeMon]

Hi Martin,

thanks for this qualified feedback.

Hmmm I am surprised about the connection of pin 1 for the 28C256 - there is a pull down missing. You are perfectly right in this point.
On my board this did work but I am not 100% sure if I tested all pages properly as I was mainly focused on page swap in general.
So there should be a resistor added if the upper region of the EEPROM is used.

For the 28C512 - I did choose not to support this EEPROM as it needs a bigger socket as well (32 pin instead of 28).
As the ROM socket is bigger than the original (24 pin) I did support all EPROMs and EEPROMs fitting into a 28 pin socket only.
But the EPROM type 27C512 fits into this socket and is supported as well. Of course does this EPROM need a pull down resistor in same way as for the 28C256.

Thanks for that great support with a software package. I have to try it out soon.

Yes the options ZX80IKIT and ZX80NMIX will come soon.
The NMIX is ready in principle but not tested yet and no boards routed yet. Schematic is finished.
It is a bit different to the realization of Grant Searle.

[Kiwisek]

But the EPROM type 27C512 fits into this socket and is supported as well. Of course does this EPROM need a pull down resistor in same way as for the 28C256.

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

Thanks for that great support with a software package. I have to try it out soon.

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.