Reversible 16K RAM
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- Posts: 2182
- Joined: Sat Nov 26, 2016 2:42 am
Reversible 16K RAM
Hi all
Has anyone done this mod on the issue one zeddy?
http://blog.tynemouthsoftware.co.uk/201 ... n.html?m=1
It looks slightly less invasive than the full blown cut the tracks option and was interested in giving it a go.
Are the address lines in the same place on an issue one?
Many thanks
Lardo
Has anyone done this mod on the issue one zeddy?
http://blog.tynemouthsoftware.co.uk/201 ... n.html?m=1
It looks slightly less invasive than the full blown cut the tracks option and was interested in giving it a go.
Are the address lines in the same place on an issue one?
Many thanks
Lardo
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
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
- 1024MAK
- Posts: 5145
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Reversible 16K RAM
On the RAM chip, yes. I can’t remember if the layout of diodes is exactly the same, but it’s not hard to work out.
Bending pins of chips out was popular in the past. Just be careful with regards to static, ensure you use an iron that has an earthed bit (unless it’s a gas or battery iron).
This method does have one disadvantage. It’s not easy to swap chips around when fault finding.
Mark
Bending pins of chips out was popular in the past. Just be careful with regards to static, ensure you use an iron that has an earthed bit (unless it’s a gas or battery iron).
This method does have one disadvantage. It’s not easy to swap chips around when fault finding.
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.
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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- Posts: 2182
- Joined: Sat Nov 26, 2016 2:42 am
Re: Reversible 16K RAM
Thanks Mark. Good points.
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
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
Re: Reversible 16K RAM
Yeap,
To be honest you need 3 wires only. A10 line is connected via L2 (link) to the new memory chip.
And don't forget about 10k resistor between pins 27 & 28.
To be honest you need 3 wires only. A10 line is connected via L2 (link) to the new memory chip.
And don't forget about 10k resistor between pins 27 & 28.
Claudius
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Re: Reversible 16K RAM
.. which is not necessary for this use case
Maybe it has been necessary for ram extensions, which had a battery (to write-protect the ram during power-off state) ...
Siggi
My ZX81 web-server: online since 2007, running since dec. 2020 using ZeddyNet hardware
http://zx81.ddns.net/ZxTeaM
http://zx81.ddns.net/ZxTeaM
Re: Reversible 16K RAM
Now to find a source of HM62256ALP chips that wont take a month to arrive..
- 1024MAK
- Posts: 5145
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Reversible 16K RAM
The currently available modern DIL 32K byte SRAM chips should work
E.g. this type LY62256PL-55LLI available from Farnell.
Not that I have actually tried this make/type yet.
Mark
E.g. this type LY62256PL-55LLI available from Farnell.
Not that I have actually tried this make/type yet.
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.
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.
Re: Reversible 16K RAM
I ordered some HM62256ALP-10s this AM with 28 pin dual-swipe sockets. If there is interest, I will sell them in the states as I ordered a few. Now I get to wait.. And wait... And wait...
Re: Reversible 16K RAM
Wellp.. My "RAM" arrived from China today. WRONG chips. I am not the proud owner of 10 "ATMEGA328P" chips.. wheeeeeee No 16K for my T/S 1000s.. No sir.
lame
lame
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- Posts: 2
- Joined: Sat Aug 03, 2019 2:47 am
Re: Reversible 16K RAM
Sorry if this is a Captain Obvious question, but I want to make sure I'm absolutely correct before starting - Link L2 also needs to be joined as well?