Hi,

The thought had crossed my mind but this needs to be as 'cheap as [potato]
chips'. (<$1)

One device that looked promising was the Dallas DS1318 but it is parallel
and has, oddly, no crystal calibration capability (considering the
accuracy provided by the subseconds counter). The requirement is for a rtc
with accuracy better than 5ppm @ 25deg C so there are two choices:

a. Better than 5ppm xtal.
b. RTC with cal option + any cheap crystal.

Currently, I use xtals that are about 20ppm (and use software cal) but
haven't had any information back regarding the cost differential between
the <5ppm and 20ppm xtals - do you think the cost would be prohibitive?

Regards,
Dan



A PIC?

Bob Ammerman
RAm Systems

----- Original Message -----
From: <dan.lloyd@GB.ABB.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Thursday, March 25, 2004 6:08 AM
Subject: [EE]: Elapsed time counters (with calibration) ?


> Hi,
>
> I've been looking around for a 32-bit time counter (to replace a BCD
real
> time clock), possibly with sub-second resolution and found some Maxim
> parts that do the job but, unfortunately, do not have any 'internal
> calibration' functionality.
>
> Other RTCs I have used have had a 512Hz output which is used to program
> the internal register to compensate for using a cheaper crystal but I
> cannot any 32-bit counter with such a feature.
>
> Anyone know of a suitable part?
>
> Regards,
> Dan

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