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From: martin@adpplz.UUCP (Martin Golding)
Newsgroups: sci.electronics
Subject: Re: Clock Chip Wanted.
Message-ID: <419@adpplz.UUCP>
Date: 30 Jan 91 01:53:41 GMT
References: <1990006@hpldsla.sid.hp.com>
Organization: ADP Dealer Services R&D, Portland, OR
Lines: 41

In <1990006@hpldsla.sid.hp.com> djw@hpldsla.sid.hp.com (David Williams) writes:

>Is there a  definitive  cheap,  easy to get clock  chip?  ...the
>type which  tells me the time, not the type that gives me a nice
>square wave!

>If not, what are people using to keep the time.  Accuracy is not
>such a big deal, battery power use,  cheapness, and  availablity
>are.

Aha, YES! The definitive clock chip is the Mostek:

MK48T12B-15
Timekeeper (tm) ram
Do Not Dispose of in Fire

It's a regulation 8k by 8 SRAM, about half again as thick. In the
top they've inserted a battery AND a crystal. The clock is sort of
resident in part of the ram. Makes interfacing easy. And if you happen
to need nearly 8k of free ram, there you are...

We use the chip in a weird little computer we make, and I've never
heard of a problem.

Some drawbacks:
 I don't know what the current draw is compared to other SRAMs. If
you're building a portable type circuit, this could be a problem.
 The increased thickness could be a problem (although we're using it
on a Q-bus board just fine).
 You have to write some software, which presupposes a cpu. Although
you could probably 'microcode' the thing with a prom and a sequencer.

If you do end up using it, e-mail me. I'd like to hear.

>David Williams
>___________________________________________________________________
>Hewlett-Packard Scientific Instruments Division (SID) /\___________

And you didn't KNOW? tsk, tsk.

Martin Golding