ZX80 3K Ram Pack memory

Discussions about Sinclair ZX80 and ZX81 Hardware
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mhudson52
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Re: ZX80 3K Ram Pack memory

Post by mhudson52 » Tue Apr 17, 2018 12:01 am

Mark, I ran your code on my 2k TS1000 with the ram pack attached and got the exact same result as you :( , so I am assuming that something in it needs to be changed to work on the TS. Like I've said, I'm dumber'n a box of rocks when it comes to this stuff.
TS 1000 bought in 1982 and brought back to life by Sir Ian

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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Tue Apr 17, 2018 12:32 am

mhudson52 wrote:
Tue Apr 17, 2018 12:01 am
Mark, I ran your code on my 2k TS1000 with the ram pack attached and got the exact same result as you :( , so I am assuming that something in it needs to be changed to work on the TS. Like I've said, I'm dumber'n a box of rocks when it comes to this stuff.
Hmm. I have a TS1000 around he somewhere. I can't remember if it works, I think it has been modified to run at 50Hz. I also have a 3k RAM pack around somewhere. I'm working late turn shifts through to Thursday, then I'm away Friday and Saturday. So it will be a while before I can dig them out. If the TS1000 works, I'll post any findings here.

Meanwhile, the schematic for the TS1000 is essentially the same as the ZX81. So can you please recheck all the connections in the 3k RAM pack. And if you have not already done so, clean the edge connector.

I was expecting the circuitry in the 3k RAM pack to treat the existing 2k RAM chip in the TS1000 the same as it treats the 1k RAM chip in the ZX80 and ZX81. The end result being a total of 4k bytes of useable RAM (it's the decoding circuit that decides the memory map, not just the RAM chips themselves).

Mark

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mhudson52
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Re: ZX80 3K Ram Pack memory

Post by mhudson52 » Tue Apr 17, 2018 1:43 am

I appreciate the offer, Mark. If this something you can do that won't put you out, the results should be interesting.

From what Charlie says of his results with his copy of my memory pack, it sounds as though it's working.

I'd place a small wager that it's just not compatible with the TS1000.

Mike
TS 1000 bought in 1982 and brought back to life by Sir Ian

Moggy
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Re: ZX80 3K Ram Pack memory

Post by Moggy » Tue Apr 17, 2018 3:03 pm

I believe one of the tracks has to be cut to make this rampack work with the 81.
I have a book entry somewhere which I will scan and post.

The entry seems to disagree with the assertion that 4k is usable on the 81,stating as it does that the internal 1k is switched out and suggesting that the 81's ram chips be used in another zx80 rampack without the full chip complement.
I have no clue either way I'm just going by the text as written.

EDIT.
As promised the book entry as described.
Attachments
zx80rampack.zip
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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Tue Apr 17, 2018 6:34 pm

Ahh, thank you Moggy :D

Mark

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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Tue Apr 17, 2018 7:39 pm

So looking at that page that Moggy helpfully provided, comparing it to a picture of a 3k RAM pack, and comparing it to the edge-connector details for both the ZX80 and the ZX81... It looks like the 3k RAM pack is linking edge-connector terminal 23B to 0V/GND. This does not matter on a ZX80, as this edge-connector contact is not used or connected to any internal circuitry. But it does matter on ZX81 and TS1000 machines, as terminal 23B on these is the circuit to control the ROM chip...

There are some nice photos here

Mark

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Re: ZX80 3K Ram Pack memory

Post by Moggy » Tue Apr 17, 2018 8:06 pm

Anytime Mark just glad to help out but just to show how dense I am I've just realised that this rampack uses static and not dynamic chips so no refresh required. DOH! :oops:

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1024MAK
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Re: ZX80 3K Ram Pack memory

Post by 1024MAK » Tue Apr 17, 2018 8:11 pm


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mhudson52
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Re: ZX80 3K Ram Pack memory

Post by mhudson52 » Wed Apr 18, 2018 3:01 am

You guys are really finding some awesome stuff. As for the mod that Moggy has unearthed, something different will probably have to done in this situation. The board design I am using is the one Marcus Brenner re-drew based on the original board. Charlie found a couple of errors that, when corrected, made it functional.

With my knowing what little I do it does make me wonder if the differences between the two boards would make them behave differently.

Here is the top layer of the board.
3K Memory Pack.JPG
Here is the original board.
Attachments
3K Memory Pack Original.JPG
3K Memory Pack Original.JPG (20.47 KiB) Viewed 424 times
TS 1000 bought in 1982 and brought back to life by Sir Ian

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msch
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Re: ZX80 3K Ram Pack memory

Post by msch » Wed Apr 18, 2018 10:38 am

mhudson52 wrote:
Wed Apr 18, 2018 3:01 am
The board design I am using is the one Marcus Brenner re-drew based on the original board. Charlie found a couple of errors that, when corrected, made it functional.
Could You please describe the errors / required fixes for the board to make it functional? I have the same PCB.
If requested I will post some images of the original RAM-Pack PCB.
ZX-Team member, Germany

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