Yes, you had to connect the L2 bridge.McKlaud wrote:A10 line is connected via L2 (link) to the new memory chip.
Reversible 16K RAM
Re: Reversible 16K RAM
Xavier ...on the Facebook groupe : "Zx81 France"(fr)
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Re: Reversible 16K RAM
A different method (cutting tracks on the PCB) is shown here (the advantage being you can use plug in a new RAM chip without having to mess about with wires on some of the pins).
This site shows details of all the extra connections including the link wire.
Mark
This site shows details of all the extra connections including the link wire.
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
Did anyone take a copy of Dave C's blog post for this upgrade? It looks like Dave's taken down his blog due to ongoing requests - which leaves me in the lurch as I was going to do this upgrade at the weekend now the Ram chip has arrived.
I know there's some more "permanent" versions available but I really don't want to cut any tracks; it's very unlikely that it'd ever be reversed anyway, but I'd prefer an option, just in case of problems.
Trevor
I know there's some more "permanent" versions available but I really don't want to cut any tracks; it's very unlikely that it'd ever be reversed anyway, but I'd prefer an option, just in case of problems.
Trevor
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Reversible 16K RAM
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
Thanks very much Mark - much appreciated.
I've now got a PDF version stored so hopefully it'll all be good.
Once again - thanks
Trevor
I've now got a PDF version stored so hopefully it'll all be good.
Once again - thanks
Trevor
- 1024MAK
- Posts: 5118
- Joined: Mon Sep 26, 2011 10:56 am
- Location: Looking forward to summer in Somerset, UK...
Re: Reversible 16K RAM
If you have any questions about this or any other 16K internal RAM modification, please ask.
Mark
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
Not the greatest start today - thought I'd make sure the machine was working before upgrading, only to find the 20+ year old telly I'd recently bought for it's analog tuning doesn't actually have an aerial socket. So - I'm going to take the zx8-ccb route initially ( I have one) - just to make sure things work then I'll do the upgrade. A minor setback - I just ran out of time due to other family "stuff".
Re: Reversible 16K RAM
I was able to successfully use a Toshiba TC55257 which, consulting its datasheet, was sold as an equivalent to the various 62256 chips commonly suggested for this mod. I found it by simply Googling "32KB SRAM DIP-28" I think. There's one left for £1.80 if you're quick!
https://www.ebay.co.uk/itm/143432785940
https://www.ebay.co.uk/itm/143432785940