[sci.electronics] Clock Chip Wanted.

djw@hpldsla.sid.hp.com (David Williams) (01/25/91)

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.

Also,    I    don't     care    if    the     output    is    in
years/months/days/hours/etc  or just  seconds  from  some  time,
there will be a million layers of software above it.

thanks,

David Williams
___________________________________________________________________
Hewlett-Packard Scientific Instruments Division (SID) /\___________
1601 California Ave, Palo Alto, CA, USA. /\______________/\________
phone: 415 857 6100. FAX: 415 852 8011  //\\____________|__________
HP-UX Mail:  djw@hpldsla.hp.com         /  \____/\____/\___________
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lairdkb@mentor.cc.purdue.edu (Kyler Laird) (01/26/91)

Geez, there are so many!  I have a Dallas Semiconductor data book that lists
16 different timekeeping devices.

Some of the distinguishing features: serial output, built in battery, NV SRAM,
watchdog circuits, alarms, EISA/ISA bus compat.

The most basic chip (DS1202) is an 8-pin DIP, counts seconds-years (day of
week) with leap year comp., 24x8 RAM, serial (3 wire) I/O, 2.0-5.5V operation,
uses <300na@2V, single/multiple-byte data transfer, optional 16-pin SOIC 
package, TTL compat., temp -40 to +85 C.  Needs 32.768 KHz crystal.

Hope that helps!

-------------------------------------------------------------------------------
Kyler Laird                  I'm  the NRA          lairdkb@mentor.cc.purdue.edu

terryb@cs.fau.edu (terry bohning) (01/27/91)

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!
> 
The Real Time Clock chip used in the PC/AT is an MC146818.  Should
be plentiful, but I don't know the cost.  Hook up an xtal and it goes.

martin@adpplz.UUCP (Martin Golding) (01/30/91)

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

djw@hpldsla.sid.hp.com (David Williams) (02/01/91)

> >David Williams
> >___________________________________________________________________
> >Hewlett-Packard Scientific Instruments Division (SID) /\___________
> 
> And you didn't KNOW? tsk, tsk.

Hay, I'm a Unix  software  engineer.  Some might say it's pretty
good I even know what a real time clock chip is!  :-)

thanks for your input.

djw@hpldsla.hp.com
From now on I'll leave out the other stuff in sci.electronics!