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> I am after designing a Real-Time Clock circuit with 8 Data output lines,
> such that at a specific time of the day it should output a set pattern of
> data on its output, hold this data at the outputs for exactly 3 hours, then
> revert to default (defined) for the rest of the day. Further, this change
> should only happen during weekdays and not weekends or public holidays. I am
> hoping to achieve this by using a RTC chip.  I am presently looking at a
> chip which I believe may be able to do this (RTC-62421). Has anyone used
> this chip before or have any information like datasheet, specs etc...? Any
> ideas or suggestions appreciated - Tks/Darrin

An RTC won't help you anything to solve your problem.
All common RTCs, including the mentioned one, provide data to
be read out of internal registers by some processor interface
(often I2C or SPI, 4-bit bus for the 62421/72421).
None of them provides parallel static data, and none of them
can be configured for particular output signals at given
conditions. Also none of them can be used as stand alone
clocks, they all need a controller for initialisation and
data readout.

What you need is a microcontroller that keeps track of the
weekday (not necessarily the complete date) and time and
generates the appropriate output signal(s).
You might *add* an RTC to avoid losing the time during power
fails.

-- 
Dipl.-Ing. Tilmann Reh
Autometer GmbH Siegen - Elektronik nach Ma�.
http://www.autometer.de