Before you start specifying any hardware, you need a good understanding of the functional requirements, and after that you need to take a look at the trade-offs you will experience selecting one device over another. The original poster has specified only two real requirements (works with 8051 and has internal battery backup).


Steve has a great point about the RTC being language-agnostic. However, remember that the ease of interfacing the RTC is going to be largely dependent on its interface and the interfaces supported by your system. For example, if your system supports I²C, an RTC using this interface might be a natural choice. However, if not, it either means you have to incorporate I²C support, either with a hardware interface or a bit-banged software solution. Neither is prohibitively difficult, but it is something to consider.


No. Examination of the DS1307 data sheet quickly reveals that this device's nonvolatile storage is supported by an external battery, which is in direct conflict with the requirements provided. This does not imply, however, that the DS1307 is a bad RTC. There are certainly a number of good reasons why the original poster might want the battery internal, ranging simple from reduced component count to benefits like the added vibration resistance benefits of a potted EDIP package.

The DS12887 meets the requirements the original poster established. However, this assumes much about the project that I don't know about (desired interface, 5V operation, etc.) It's worth a look if for no other reason that it provides an example of some of the (occasionally very useful) features that are available in a more feature-rich RTC.

Steve is right about about Maxim/Dallas. They have an impressive array of timekeeping products; starting on their Real-Time Clocks page would be a good idea. After that, start flushing out your list of requirements and then visit their Timekeeping & Real-Time Clocks Selector to find a suitable device.

--Sasha Jevtic