Hello, I'd like to replace the Z80 in an Issue 3 48K Spectrum and figured I might as well get a version with the built in 32K of RAM.
The instructions are a little sparse and just say to remove the original upper ram. Is it enough just to remove the RAM chips, or do any changes need to be made to the other chips that are added when upgrading to 48K?
Thanks
Replacing Z80 with SRAM version
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Ast A. Moore
- Rick Dangerous
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Re: Replacing Z80 with SRAM version
I’m sorry, but what’s a Z80 with “32K of built-in RAM”?
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Replacing Z80 with SRAM version
I'm guessing it's this one:
https://www.ebay.com/itm/393315688828
In which case, yes, just remove the upper RAM and drop this in place of the Z80.
Is it using a CPLD to emulate a Z80 or is that a genuine Z80 in a different form factor?
https://www.ebay.com/itm/393315688828
In which case, yes, just remove the upper RAM and drop this in place of the Z80.
Is it using a CPLD to emulate a Z80 or is that a genuine Z80 in a different form factor?
Last edited by Pobulous on Wed May 11, 2022 9:27 am, edited 1 time in total.
Re: Replacing Z80 with SRAM version
The problem with the Z80SRAM is that it is a little higher than the Z80 CPU. So you could have problems with an RubberKey-case.
It is better to solder it without an socket
You have to remove all the "Upper RAM's" but not the IC 23 - IC 26. No other changes (eventually remove the CPU socket).
I offer such a board on ebay 'till sunday
https://www.ebay.de/itm/304479884020
It is better to solder it without an socket
You have to remove all the "Upper RAM's" but not the IC 23 - IC 26. No other changes (eventually remove the CPU socket).
I offer such a board on ebay 'till sunday
https://www.ebay.de/itm/304479884020
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Ast A. Moore
- Rick Dangerous
- Posts: 2644
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Replacing Z80 with SRAM version
This is just the RAM module itself with no CPU on the board.PeterJ wrote: ↑Wed May 11, 2022 9:18 am Is it this @Ast A. Moore?
https://rc2014.co.uk/modules/retired/32k-ram/
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
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Ast A. Moore
- Rick Dangerous
- Posts: 2644
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Replacing Z80 with SRAM version
Oh, interesting. I assume, since it’s designed with the Speccy in mind, it already puts the RAM at address $8000. In that case, sure, it could be used instead of the original RAM. I’m not sure why one would want to use it, though. There’s a slight chance that you might lose compatibility with a few programs.Pobulous wrote: ↑Wed May 11, 2022 9:23 am I'm guessing it's this one:
https://www.ebay.com/itm/393315688828
In which case, yes, just remove the upper RAM and drop this in place of the Z80.
Is it using a CPLD to emulate a Z80 or is that a genuine Z80 in a different form factor?
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Replacing Z80 with SRAM version
Thanks for the suggestions.
It's this one - https://lotharek.pl/productdetail.php?id=263
It's a Zilog Z80 so I'm guessing its just in a different package.
As for the why, I want to replace the Z80 so may aswell kill two birds with one stone.
Thanks
It's this one - https://lotharek.pl/productdetail.php?id=263
It's a Zilog Z80 so I'm guessing its just in a different package.
As for the why, I want to replace the Z80 so may aswell kill two birds with one stone.
Thanks
Re: Replacing Z80 with SRAM version
I had no idea such a thing existed, what a great idea. 
I first thought before I fully read the topic it was a generic Z80 with 32K of Ram but not Spectrum specific, ie just a tiny chip sized board with the CPU and some control logic and the Ram itself.
What would be really neat (possibly not practical) would be one that had -all- the ram onboard, drop in the CPU + possibly make a few wire links if needed = end of memory issues.
I first thought before I fully read the topic it was a generic Z80 with 32K of Ram but not Spectrum specific, ie just a tiny chip sized board with the CPU and some control logic and the Ram itself.
What would be really neat (possibly not practical) would be one that had -all- the ram onboard, drop in the CPU + possibly make a few wire links if needed = end of memory issues.
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Ast A. Moore
- Rick Dangerous
- Posts: 2644
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Replacing Z80 with SRAM version
Not easily achieved, I’m afraid. The lower 16K of RAM are shared between the CPU and the ULA, and the ULA governs access to it (creating what is known as memory contention).
There are lower-RAM replacement boards, however.
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Replacing Z80 with SRAM version
Thanks. I did half suspect that.Ast A. Moore wrote: ↑Wed May 11, 2022 2:24 pm Not easily achieved, I’m afraid. The lower 16K of RAM are shared between the CPU and the ULA, and the ULA governs access to it (creating what is known as memory contention).
There are lower-RAM replacement boards, however.
The next step would be to start putting things like the ULA on it so the lower ram actually worked properly (not sure how timing would be with no contention at all) and before you know where you are you'd end up with a FPGA or something similar aka "Speccy on a chip"-
Ast A. Moore
- Rick Dangerous
- Posts: 2644
- Joined: Mon Nov 13, 2017 3:16 pm
Re: Replacing Z80 with SRAM version
Exactly!
Every man should plant a tree, build a house, and write a ZX Spectrum game.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Author of A Yankee in Iraq, a 50 fps shoot-’em-up—the first game to utilize the floating bus on the +2A/+3,
and zasm Z80 Assembler syntax highlighter.
Re: Replacing Z80 with SRAM version
An interesting solution would be a z80 with 64K of ram, of which 48K is mapped, and the reads come from the SRAM and the writes go out to the bus as well. Then a Spectrum could boot and run correctly despite a RAM fault in most cases, and would help in troubleshooting since you may get a picture and at least could make the computer function, as long as the ULA was working correctly.
Anyway, interesting board... Thanks for posting about it.
Anyway, interesting board... Thanks for posting about it.