A project I'm working on will likely go into the 1,000's of units. The design calls for an 8051 and a RTC.
I was planning to use the DS1307 because I'm familiar with it, it fits the bill, and I already have the code for it. Plus, it's pretty bullet-proof.
And even though we've used it in lots of prior projects, we never really had a need to use the skimpy 56 bytes of NV-SRAM it provides.
This project happens to be a candidate. If these bytes didn't exist, we'd probably just select a micro with EEPROM and that'd be it, or use an outboard serial EEPROM. (This app does not require so many writes as to wear out an EEPROM. We're just storing some options variables, that the user can modify on initial installation.)
So my question: Is there any reason we shouldn't use the DS1307 registers for long-term, unattended memory storage? Anybody doing this now? And having good results? I would really like to save the $ $ on the less-capable 8051's. (i.e., without EEPROM capability).
We're decided on a CR2032 coin cell, and the 106K holder from Keystone (which is a FANTASTIC holder for this battery! Nice and tight!) The battery should last for many years, and it's not a problem if the memory dumps when replacing the cell.
The application will be inside a work truck, permanently attached, so bumps and bruises are expected... I should also mention that even if the memory is lost, the device will still work, but will do so in a factory-default sort of way - which will likely not be that objectionable to the customer.(?)
Anybody have any thoughts about EEPROM vs. NV-SRAM or does it really make any difference?