2KB memory in a 1KB ZX81

Discussions about Sinclair ZX80 and ZX81 Hardware
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Whopper
Posts: 6
Joined: Mon Jan 22, 2018 8:38 pm

2KB memory in a 1KB ZX81

Post by Whopper » Mon Jan 22, 2018 8:54 pm

Hi All,

I've tried searching but couldn't find any results.

I have just opened up my ZX81 and fins that it has an NEC D4016D 24 pin memory chip. LK1 is connected NIT LK2. So A10 is held at +5v.

Is this a usual state of affairs, or just another case of using whatever was in the stores at the time?

Can I reposition the link (LK1) to LK2 and get another 1KB of memory?

I appreciate and help / advice given,

Thanks,

Whopper
You woke me for THAT!!!

McKlaud
Posts: 41
Joined: Tue Dec 19, 2017 10:02 pm
Location: St Albans, UK

Re: 2KB memory in a 1KB ZX81

Post by McKlaud » Mon Jan 22, 2018 10:56 pm

NEC D4016D is 2KB (2048words x 8bits) Static RAM chip. You will not risk anything if you remove LK1 and put the LK2 in.

2KB was a standard in any TS1000. I would not be surprised if your board is one of Issue 3 boards but Sinclair was short with supplies to UK market and they used anything what they could find in the store.
Claudius
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1024MAK
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Joined: Mon Sep 26, 2011 10:56 am
Location: Looking forward to summer in Somerset, UK...

Re: 2KB memory in a 1KB ZX81

Post by 1024MAK » Tue Jan 23, 2018 3:35 pm

Whopper wrote:
Mon Jan 22, 2018 8:54 pm
I've tried searching but couldn't find any results.

I have just opened up my ZX81 and fins that it has an NEC D4016D 24 pin memory chip. LK1 is connected NIT LK2. So A10 is held at +5v.

Is this a usual state of affairs, or just another case of using whatever was in the stores at the time?

Can I reposition the link (LK1) to LK2 and get another 1KB of memory?
Hello Whopper

Welcome to our forum.

The simple answer is, yes, moving the link wire should get you an extra 1k byte of available RAM.
But before you change it, it would be nice if you can post up a good quality photo of your ZX81 ;)

Mark

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