Eprom found inside my Zx81.. normal?

Discussions about Sinclair ZX80 and ZX81 Hardware
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RS232
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Eprom found inside my Zx81.. normal?

Post by RS232 »

Hi all, can anyone confirm was this a regular fit by Sinclair?

See attached screen shot with the two red wires indicating modification.

Thanks!
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20190323_194230.jpg
Lardo Boffin
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Re: Eprom found inside my Zx81.. normal?

Post by Lardo Boffin »

I have one of these. :D
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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1024MAK
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Re: Eprom found inside my Zx81.. normal?

Post by 1024MAK »

Yes.

Manufacturers of EPROMs could supply them preprogrammed to the customers requirements and when Sinclair ran out of mask programmed ROM chips, occasionally this was done.

If you look, the EPROM has ZX81 screen printed on it.

The wires are because the EPROM used has some connections that are different to that of a ROM chip.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
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XavSnap
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Re: Eprom found inside my Zx81.. normal?

Post by XavSnap »

:lol:
- "64k ZX81"
- "RTI" Eeprom… ???

Just a fake picture (it's a sticker added on the component) and the background (grey) had been rerive from a deleted sérial number(white sticker in the UV window deleted too! !photoshop! ).
It's a good Joke.
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
Lardo Boffin
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Joined: Sat Nov 26, 2016 2:42 am

Re: Eprom found inside my Zx81.. normal?

Post by Lardo Boffin »

I have one with similar writing.

https://sinclairzxworld.com/viewtopic.p ... 008#p32174

Rubbish photo but you can just make it out.
ZX80
ZX81 iss 1 (bugged ROM, kludge fix, normal, rebuilt)
TS 1000 iss 3, ZXPand AY and +, ZX8-CCB, ZX-KDLX & ChromaSCART
Tatung 81 + Wespi
TS 1500 & 2000
Spectrum 16k (iss 1 s/n 862)
Spectrum 48ks plus a DIVMMC future and SPECTRA
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1024MAK
Posts: 5101
Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: Eprom found inside my Zx81.. normal?

Post by 1024MAK »

64K as in 8k x 8 bit bytes, or 65536 bits of storage...

Never underestimate the ability of the marketing department to big-up the numbers :lol:

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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RS232
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Joined: Fri Apr 05, 2019 8:57 pm

Re: Eprom found inside my Zx81.. normal?

Post by RS232 »

XavSnap wrote: Mon Apr 08, 2019 8:56 pm :lol:
- "64k ZX81"
- "RTI" Eeprom… ???

Just a fake picture (it's a sticker added on the component) and the background (grey) had been rerive from a deleted sérial number(white sticker in the UV window deleted too! !photoshop! ).
It's a good Joke.
This wasn't a Photoshop, real life Sinclair weird moment i guess
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RS232
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Re: Eprom found inside my Zx81.. normal?

Post by RS232 »

Anybody know of any other ROM's that can fit our humble ZX81 board?
Moggy
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Re: Eprom found inside my Zx81.. normal?

Post by Moggy »

A 2764 EPROM with a bit of pin re-wiring is one commonly used.

You can program this with either Husband ZXforth or Asmic (I don't know too much about this one) then there's the recently developed double speed ROM or you could program the ZX80 ROM code into it and with the help of five resistors soldered to the CPU turn your ZX81 into a ZX80.
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1024MAK
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Re: Eprom found inside my Zx81.. normal?

Post by 1024MAK »

27256 / 27C256 can be shoehorned in with a bit of extra wire and a bit of extra circuitry, then you have 8k bytes to use for your own “permanent” machine code (or other data).

It should also be possible to fit more modern EEPROM chips, but as far as I know, no one has tried yet. You do have to ensure that such a device never has it’s write control line go to the active state (because the ZX81 BASIC ROM code actually tries to write to some parts of the ROM!)

There is a flash ROM on an adaptor board that is a direct plug in replacement. This comes from RWAP on Sell My Retro. Ask Rich (RWAP) for more information.

Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor Buffer Amp

:!: Standby alert :!:
There are four lights!
Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb :!:
Looking forward to summer later in the year.
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