Best solution for expanding ram to 128k on a zx48k?
Best solution for expanding ram to 128k on a zx48k?
Thanks for accepting me here. Been tinkering with my zx48k (issue 2) and done the following repairs/upgrades:
-caps replaced (also inside psu)
-regulator replaced
-s-video mod done (replaced rf modulator internals)
-new keyboard membrane
Now the only thing I want is to expand the ram to (at least) 128k to be able to run the latest homebrew stuff There are some internal and external concepts, but some of them are really old etc. I know the space is really constrained inside the speccy but I'm willing to try this out. I love the design of the 48k and thus would not want to have a later model (not even the toastrack).
What is currently the best way to expand the ram of a issue 2 zx48k? If possible the expansion would be compatible with Divide etc modern hw.
Thanks
-caps replaced (also inside psu)
-regulator replaced
-s-video mod done (replaced rf modulator internals)
-new keyboard membrane
Now the only thing I want is to expand the ram to (at least) 128k to be able to run the latest homebrew stuff There are some internal and external concepts, but some of them are really old etc. I know the space is really constrained inside the speccy but I'm willing to try this out. I love the design of the 48k and thus would not want to have a later model (not even the toastrack).
What is currently the best way to expand the ram of a issue 2 zx48k? If possible the expansion would be compatible with Divide etc modern hw.
Thanks
- 1024MAK
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Re: Best solution for expanding ram to 128k on a zx48k?
I presume you mean the original rubber key model?
Actually fitting larger capacity DRAM chips is not too much of a problem. The problem is adding the circuitry to provide the bank switching capability, especially if you want it to be configured to be the same as in a ZX Spectrum 128k (Toastrack)/+2 (grey). Or to be configured to be the same as in a ZX Spectrum +2A / +2B (both in a black case) or a +3 / +3B.
In all cases, you will need some programmable logic device (or devices). In the past GAL chips were popular. But a lot of the hobby friendly chips have been discontinued. You can still get some from eBay, but with the usual risks of such a marketplace.
Mark
Actually fitting larger capacity DRAM chips is not too much of a problem. The problem is adding the circuitry to provide the bank switching capability, especially if you want it to be configured to be the same as in a ZX Spectrum 128k (Toastrack)/+2 (grey). Or to be configured to be the same as in a ZX Spectrum +2A / +2B (both in a black case) or a +3 / +3B.
In all cases, you will need some programmable logic device (or devices). In the past GAL chips were popular. But a lot of the hobby friendly chips have been discontinued. You can still get some from eBay, but with the usual risks of such a marketplace.
Mark
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ZX81 Chip Pin-outs
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Step up to red alert. Sir, are you absolutely sure? It does mean changing the bulb
Looking forward to summer being good this year.
Re: Best solution for expanding ram to 128k on a zx48k?
Hi Mark, the s-video mod works great1024MAK wrote: ↑Tue Jan 08, 2019 3:31 pm I presume you mean the original rubber key model?
Actually fitting larger capacity DRAM chips is not too much of a problem. The problem is adding the circuitry to provide the bank switching capability, especially if you want it to be configured to be the same as in a ZX Spectrum 128k (Toastrack)/+2 (grey). Or to be configured to be the same as in a ZX Spectrum +2A / +2B (both in a black case) or a +3 / +3B.
In all cases, you will need some programmable logic device (or devices). In the past GAL chips were popular. But a lot of the hobby friendly chips have been discontinued. You can still get some from eBay, but with the usual risks of such a marketplace.
Mark
I also realised the ram chip(s) are not the problem, but the logic is. There seems to be GALs available on Ebay, but the mileage might not be perfect with some of them... I found this "universal" 128k rebuild:
https://hw.speccy.cz/128krebuild.html
and this external one:
https://velesoft.speccy.cz/zx/external_ ... /index.htm
They both use GALs.
I'm really not sure (or technically competent enough) to evalute how I want the ram to be configured (ZX Spectrum 128k (Toastrack)/+2 (grey) or ZX Spectrum +2A / +2B (both in a black case) or a +3 / +3B). Could you please enlighten me on this? I just thought "if there's 128k ram, then there is
Thanks one again Mark for your time helping others out
Re: Best solution for expanding ram to 128k on a zx48k?
Hi Mark,
While this was true for several years microchip technologies is now producing chips starting with ATF. ATF16V8 for example in DIP, PLCC, SOP...
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: Best solution for expanding ram to 128k on a zx48k?
Thanks for that, it seems this is pin compatible with the GALs used in the designs:Hi Mark,
While this was true for several years microchip technologies is now producing chips starting with ATF. ATF16V8 for example in DIP, PLCC, SOP...
https://www.mouser.fi/datasheet/2/268/d ... 180745.pdf
But what about the code? There seems to be these 3 files for the GAL regarding the internal 128k mod: p2_gal, p2_gal.eqn, p2_gal.jed
That's compiled assembly code, right? Sorry, this is completely new area for me
- 1024MAK
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- Joined: Mon Sep 26, 2011 10:56 am
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Re: Best solution for expanding ram to 128k on a zx48k?
Careful. Only CPUs, microprocessors and microcontrollers execute assembly code.
In programmable logic devices, be they PAL, GAL, CPLD or FPGA devices, what you are actually see is device configuration information. This tells the programmer how to configure the logic gates in the device so that it will perform the logic functions that you want.
.eqn is the human readable file with the required equations and other details.
.jed is the JEDEC file and it contains all the details that the programmer needs to program the chip.
For more information see these links:
https://www.uchobby.com/index.php/2008/ ... ics-hobby/
http://sss-mag.com/pdf/PLDTUTOR.pdf
Mark
In programmable logic devices, be they PAL, GAL, CPLD or FPGA devices, what you are actually see is device configuration information. This tells the programmer how to configure the logic gates in the device so that it will perform the logic functions that you want.
.eqn is the human readable file with the required equations and other details.
.jed is the JEDEC file and it contains all the details that the programmer needs to program the chip.
For more information see these links:
https://www.uchobby.com/index.php/2008/ ... ics-hobby/
http://sss-mag.com/pdf/PLDTUTOR.pdf
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
- 1024MAK
- Posts: 5302
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Best solution for expanding ram to 128k on a zx48k?
The differences between these machines are described in detail hereemuola wrote: ↑Tue Jan 08, 2019 5:06 pmI'm really not sure (or technically competent enough) to evalute how I want the ram to be configured (ZX Spectrum 128k (Toastrack)/+2 (grey) or ZX Spectrum +2A / +2B (both in a black case) or a +3 / +3B). Could you please enlighten me on this? I just thought "if there's 128k ram, then there is
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
- 1024MAK
- Posts: 5302
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Best solution for expanding ram to 128k on a zx48k?
Hi Paul
Ahh, yes.
A lot of hobby projects are/were based on the Lattice versions of the GAL chips. That is the line that has been discontinued. Being a popular line of parts, it’s not difficult to find inexpensive third party programmers for the Lattice GAL chips.
I have not tried any Microchip / ATMEL GAL chips myself yet. Do they use the same programming arrangements as Lattice chips? If not, which programmer do you use? Or, do you know if there is a list of suitable programmers somewhere?
Mark
ZX81 Variations
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
ZX81 Chip Pin-outs
ZX81 Video Transistor 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 being good this year.
Re: Best solution for expanding ram to 128k on a zx48k?
My programmer is a tl866
I use latest lattice settings without problems.
I am not sure whether I have a deviceID check disabled or if it's on defaults.
Kind regards Paul
I use latest lattice settings without problems.
I am not sure whether I have a deviceID check disabled or if it's on defaults.
Kind regards Paul
In theory, there is no difference between theory and practice. But, in practice, there is.
Re: Best solution for expanding ram to 128k on a zx48k?
Thanks, this makes all this stuff more clear1024MAK wrote: ↑Wed Jan 09, 2019 10:41 am Careful. Only CPUs, microprocessors and microcontrollers execute assembly code.
In programmable logic devices, be they PAL, GAL, CPLD or FPGA devices, what you are actually see is device configuration information. This tells the programmer how to configure the logic gates in the device so that it will perform the logic functions that you want.
.eqn is the human readable file with the required equations and other details.
.jed is the JEDEC file and it contains all the details that the programmer needs to program the chip.
For more information see these links:
https://www.uchobby.com/index.php/2008/ ... ics-hobby/
http://sss-mag.com/pdf/PLDTUTOR.pdf
Mark
Ok, so if I would like my zx48k behave like the toast track ram wise, how would it affect the actual upgrade? Sorry, that paging thingy got me kinda confused. I noticed that for example many games using ay for music require 128k minimum. I was planning to use the Melodik2 for the ay sound. On a 128k the additional ram is paged on top of the 16k as it says. So, to achieve that in practice on my 48k, what would be the easiest way?1024MAK wrote: The differences between these machines are described in detail here