Genuine DS1210 NVRAM controllers

[Slothie]

Originally Posted by SiriusHardware

Unfortunately, 50Hz-AC is not one of the signals available on the MK14 rear edge connector, not even on the issue VI.

That might have to be added to the rev 1.3 wish list

[Mark1960]

I remembered wrong, I didn’t find the schematic, but looking at an old set of notes it was using a comparator on the unregulated supply feed to the 5v regulator, so it would give advanced warning of power fail.

[SiriusHardware]

I think it might be too installation specific, there's no standard MK14 power supply, or rather there is but almost no-one bought one. I use a very well regulated 7.5V linear supply so there would be almost no ripple for such a circuit to detect the absence of.

[Mark1960]

It wasn’t detecting the ripple, just a comparator to detect the input to the regulator dropping, this reset the z80 before the 5v supply started to drop.

[SiriusHardware]

That's OK as long as the input supply voltage has generous headroom between the unregulated input voltage and the minimum input voltage so you could aim for a shutdown input voltage of (say) 8V if the unregulated input is normally no less than 9V on full load.

On mine, where I have the difference between input and output volts as low as possible I would have to set / choose the threshold voltage very carefully.

[Timbucus]

The PE Champ has a discrete component Power Fail detect and Battery backup for its low power 5101 RAM chips. You can see this in the diagram at the bottom of Page 108 of PE October 1977

https://worldradiohistory.com/UK/Pra...cs-1977-10.pdf

It basically controls one of the Intel 3205 1 of 8 decoder chips enable lines (E2 pin 5) so the RAM's cannot be selected.

For those who do not know this old Intel chip this site has a link to its datasheet - along with other geat resources:

https://inttel.blogspot.com/2011/01/...processor.html

[Slothie]

I remember buying that issue of PE in WH Smiths I was hoping to build the mastermind game, but never did. I wanted to build the Champ too, but that would have involved persuading my dad to finance it, and that wasn't going to happen because he wssn't into digital electronics at the time.

[Timbucus]

I am trying to gather the bits in the background to build one - if anyone has the acres of veroboard or soldercon pins needed give me a shout - I will start a thread. EDIT:The PE Champ I mean...

[Mark1960]

Originally Posted by Timbucus

It basically controls one of the Intel 3205 1 of 8 decoder chips enable lines (E2 pin 5) so the RAM's cannot be selected.

The power fail circuit goes direct to the active high chip enables of the 5101 ram. Its not clear if the 74L00 is powered from the battery backup supply, it probably isn’t.

[Michael - K8LH]

Just wanted to report that I received a batch of five (5) DS1210 ICs from this Vendor ($4.03, including shipping) and all five look new and tested ok.

Regards, Mike

[Phil__G]

Weird, they wont ship to the UK!