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Reversible 16K RAM

Posted: Thu Dec 06, 2018 8:43 am
by Lardo Boffin
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

Re: Reversible 16K RAM

Posted: Thu Dec 06, 2018 11:34 am
by 1024MAK
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

Re: Reversible 16K RAM

Posted: Thu Dec 06, 2018 3:42 pm
by Lardo Boffin
Thanks Mark. Good points.

Re: Reversible 16K RAM

Posted: Thu Dec 06, 2018 11:33 pm
by McKlaud
Yeap,

To be honest you need 3 wires only. A10 line is connected via L2 (link) to the new memory chip.

Image

And don't forget about 10k resistor between pins 27 & 28.

Image

Re: Reversible 16K RAM

Posted: Fri Dec 07, 2018 10:17 am
by siggi
McKlaud wrote:
Thu Dec 06, 2018 11:33 pm
And don't forget about 10k resistor between pins 27 & 28.
.. 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