ZXPands and ZXpand-AY modules back in stock

ZX80 / ZX81 hardware and software offered for sale or swapping
RWAP
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ZXPands and ZXpand-AY modules back in stock

Post by RWAP » Thu Jun 12, 2014 5:14 pm

With many thanks to SirMorris, we now have some more ZXpand Interfaces and ZXpand-AY Modules in stock:

ZX81 ZXpand interfaces:
http://www.sellmyretro.com/offer/detail ... rface-2435

ZX80 ZXpand Interfaces:
http://www.sellmyretro.com/offer/detail ... rface-3754

ZXpand-AY Modules:
http://www.sellmyretro.com/offer/detail ... odule-2331

:D

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Re: ZXPands and ZXpand-AY modules back in stock

Post by sirmorris » Thu Jun 12, 2014 5:59 pm

/me wipes sweat and solder flux from brow

RWAP
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Re: ZXPands and ZXpand-AY modules back in stock

Post by RWAP » Thu Jun 12, 2014 8:25 pm

By the way, have you tried one with a ZX80Core ??

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Re: ZXPands and ZXpand-AY modules back in stock

Post by 1024MAK » Thu Jun 12, 2014 10:37 pm

RWAP wrote:By the way, have you tried one with a ZX80Core ??
Sell My Retro wrote:ZX80 computers with internal RAM upgrades may not be compatible. Contact us for advice.
:D

Mark

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PokeMon
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Re: ZXPands and ZXpand-AY modules back in stock

Post by PokeMon » Fri Jun 13, 2014 1:51 pm

Yes - would be nice to hear about restrictions using ZXpand.
Internal RAM can be limited by using a smaller RAM.
So the ZX80CORE can be held exactly like a real ZX80.

The question is, what is important for the ZXpand to work on a ZX80 and how it is linked in the system (ROM) ?

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Re: ZXPands and ZXpand-AY modules back in stock

Post by sirmorris » Fri Jun 13, 2014 2:10 pm

Because an unmodified ZX80 doesn't have !ROMCS on the edge connector you need to replace the internal ROM. There is a jumper on ZXp which disables the overlay ROM, and restricts RAM to 16k. ZXp pulls !RAMCS to 5V so any internal RAM is disabled (assuming it honours !RAMCS) but I guess even if it doesn't then you'd just get both memories working in parallel. I suspect that might not be optimal.

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PokeMon
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Re: ZXPands and ZXpand-AY modules back in stock

Post by PokeMon » Fri Jun 13, 2014 2:55 pm

Okay - understand.
To be sure: The ZX80CORE has /ROMCS on the connector (if J99 is set) - so if this signal is provided (like in the ZX81 manner with an appropriate resistor), there is no ROM change needed because the internal can be switched off with pulling ROMCS high. So this might be more easy than in a original ZX80, I think.

About the RAM - this can be switched off with the /RAMCS signal which is also available on original ZX80 in the same way.
I think this would work parallel with internal and external RAM together but might result in a higher currency consumption and would not propose it.

There is just one small mechanical problem with the video chinch socket which is in the same position as the RF socket on original ZX80 and might conflict when attaching ZXpand. So here might an extender be useful or providing a second chinch connector somewhere else or a cable with chinch connector coming out. :?

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Re: ZXPands and ZXpand-AY modules back in stock

Post by sirmorris » Fri Jun 13, 2014 4:15 pm

ZXpand also has a ROM bank select so you can have the '80 and '81 ROMs in a 16k chip. It's software switchable. You're right about the physical issues Karl, there are extender cables available which will mitigate this problem.

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Re: ZXPands and ZXpand-AY modules back in stock

Post by oscar » Tue Jun 17, 2014 5:16 am

I bought one of the earlier (issue 1) ZXPands. Is there somewhere I can find out what the differences are between different issues, so I know if I should consider buying one of these new ones?

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Re: ZXPands and ZXpand-AY modules back in stock

Post by RWAP » Tue Jun 17, 2014 12:12 pm

I stand to be corrected, but as far as I know there is no real difference between the issue 1 and issue 3 in operation terms.

The issue 3 boards were slightly re-designed to make assembly easier and to get rid of those extra two pins on the PIC socket (which were used by the ZXpand-AY).

The ZXpand-AY was then modified with a wire to replace the necessity for those two extra pins - so if you plug a ZXpand-AY into an issue 3 board, you see the two pins dangling in mid air. You can still use these with the original issue 1 ZXpand, by snipping the small wire link on the back of the ZXpand-AY.

:D

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