I'd advice checking the Y2K status of the MC146818 if you are designing a product for production.

Is searched for the MC146818 on the Motorola Semicondor page and got the following page suggesting a questionable Y2K update status. That page dated May 1999 may be a forgotten homepage remnant but you better find out.

http://mot-sps.com/y2k/realtimeclocks.html

Is there any particular reason for using that RTC? It doesn't look to economical to me. While it has a nice parallel interface if you already are using your 8051 in that configuration... a quick ap-note I viewed look like it required a lot of external circuitry to make it run after power drops.

http://www.mot-sps.com/mcu/docum...an894a.pdf

For a RTC, I still use the old I2C bus DS1307.

-Jay C. Box