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From: henry@zoo.toronto.edu (Henry Spencer)
Subject: Re: HELP: MC146818A Real Time Clock Standby Mode
Message-ID: <C5uCDu.1Ip@zoo.toronto.edu>
Date: Wed, 21 Apr 1993 15:58:40 GMT
References: <1r0b69INN5ct@flash.pax.tpa.com.au>
Organization: U of Toronto Zoology
Lines: 20

In article <1r0b69INN5ct@flash.pax.tpa.com.au> mgregory@flash.pax.tpa.com.au (Martin John Gregory) writes:
>I am having trouble obtaining the specified standby current drain from
>a MC146818A Real Time Clock...
>lowest current drain I can acheive at 3.7V Vcc is 150uA.  This is
>three times the specified MAXIMUM...
>1) Made sure that RESET/ is asserted for Trlh after powerup, and AS is
>   low during this time.
>2) Made sure that there is a cycle on AS after the negation of RD/ or
>   WR/ during which STBY/ was asserted...

Are any of the inputs to the chip coming from TTL?  Standby-drain specs
for CMOS chips typically apply only if inputs are pulled all the way down
to zero or all the way up to Vcc.  TTL isn't good at doing the former and
it won't do the latter at all without help from pullup resistors.  This
sort of thing can easily multiply power consumption by a considerable
factor, because the CMOS transistors that are supposed to be OFF aren't
all the way hard OFF.
-- 
All work is one man's work.             | Henry Spencer @ U of Toronto Zoology
                    - Kipling           |  henry@zoo.toronto.edu  utzoo!henry
