RTC RTC DS3234
CR1225
http://www.l8ter.com/?p=375
http://japan.maximintegrated.com/app-notes/index.mvp/id/5413
http://japan.maximintegrated.com/design/techdocs/app-notes/index.mvp/id/21/c/%E3%83%AA%E3%82%A2%E3%83%AB%E3%82%BF%E3%82%A4%E3%83%A0%E3%82%AF%E3%83%AD%E3%83%83%E3%82%AF#c21
http://japan.maximintegrated.com/design/techdocs/tutorials/
http://www.switch-science.com/catalog/539/
http://www.ne.jp/asahi/o-family/extdisk/DS3234RTC/DS3234RTCm_jp.pdf
https://www.sparkfun.com/products/10160
https://www.sparkfun.com/datasheets/BreakoutBoards/DeadOn%20RTC%20-%20DS3234%20Breakout-v11.pdf
http://dlnmh9ip6v2uc.cloudfront.net/datasheets/BreakoutBoards/DS3234_Example_Code.pde
https://www.sparkfun.com/datasheets/BreakoutBoards/DS3234.pdf
http://japan.maximintegrated.com/datasheet/index.mvp/id/4051