Content originally posted in LPCWare by fjrg76 on Fri Apr 17 16:10:01 MST 2015
Yep, that's awkward. When the term "RTC" is read one thinks it's a real "real time clock", but it's not. Maybe you are looking for a "RTC with independent power domain". Some chips include that option, but others don't.
The RTC in the LPC1227 is just a periodic interrupt, with no other capabilities (alarms, day of time, etc.). Perhaps it's too late, but there are cheap and nice chip-off RTCs, like MCP9700, that costs under a dollar.
Another turn-around is that you power the chip with two voltage sources, the main one as usual, and other from a backup battery that powers the chip whenever the main supply has gone. At hardware level only a couple of shottky diodes are needed, whilst in software you must turn the chip off (entering to the lowest power saving profile) so it doesnt' drain the backup battery.
