Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Posting-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!henry
From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: sci.electronics,comp.unix.wizards
Subject: Re: time of year clock chips
Message-ID: <8101@utzoo.UUCP>
Date: Sat, 30-May-87 22:02:33 EDT
Article-I.D.: utzoo.8101
Posted: Sat May 30 22:02:33 1987
Date-Received: Sat, 30-May-87 22:02:33 EDT
References: <16819@amdcad.AMD.COM>, <2201@hoptoad.uucp>
Organization: U of Toronto Zoology
Lines: 25

>     I would watch out for chips that have the old daylight savings time 
> programmed into them.  I know of none that are on the current time 
> standard.

I recall none that are aware of daylight savings at all; that is usually
left to the software, with good reason -- too much local variation.  (My
old home town, Saskatoon, ignores the whole stupid business and is on CST
year round.  Why did I come to Toronto... :-))

A subtle point that a number of the chips don't get quite right, by the way,
is the possibility that leap years are not the ones with numbers divisible
by 4.  One chip -- I think it's the Oki one -- has a two-bit register that
you set to indicate the leap-year phase; none of the others do.  All users
of the Gregorian calendar agree (I think) on which years are leap years, but
they do not all agree on what numbers those years have.  The obvious case in
point is Japan, where traditional year numbering is referenced to the date
the current Emperor took the throne.  I'd guess that the Oki chip is the only
one designed in Japan.

(Of course, you can fudge around this in software by just using a different
year as the origin year, since none of these chips have a full four-digit
year register anyway...)
-- 
"There is only one spacefaring        Henry Spencer @ U of Toronto Zoology
nation on Earth today, comrade."   {allegra,ihnp4,decvax,pyramid}!utzoo!henry