>Is there anyone who has any suggestions on how to use
>a realtime clock.  I need to use it for datalogging.
>I am a student and need to do a project on
>datalogging.

If you check the PICLIST software archives, I have posted some code that you
can use to set the time on an RTC chip, as well as read the current time in
years, days, months, hours, minutes, and seconds.  It uses four pins to
control the RTC.

The clock chip itself was an NJU6355 chip available from Digi-Key for a few
dollars.

And I've even posted the link... see what I nice guy I am?

http://www.piclist.com/techref/microchip/nju6355rtc-dv.htm


In terms of the logistics of logging people in and out, you could use the
internal EEPROM data memory for storing the time variables to whatever
extent you need (days, hours, etc.)  Have the user enter a "PIN" number and
divide up your available EEPROM data space to accomodate as many users as
possible, based on the extent of the time variable storage space that is
required.

e.g. if you require 4 bytes of time variable space (days, hours, minutes,
seconds), then you could have up to 12 users (4 bytes + 1 byte for each
user's PIN * 12 users = 60 bytes.  Maximum of 64 bytes available for 16F84.)

Depending on the security required (if you don't want people to log one
another in or out), you may have to parse the PIN to accept digits in a
specific order.

--Andrew

_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com/intl.asp

--
http://www.piclist.com hint: The PICList is archived three different
ways.  See http://www.piclist.com/#archives for details.