SH7750_08 Datasheet, PDF (420/1162 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

Section 11 Realtime Clock (RTC)
3. Use the following method to write to an RTC register.
Read all writeable counter registers (1)
Write 0 to RCR2.RTCEN
Read all writeable counter registers (2)
Compare the values of (1) and (2)
Are the compared values valid? ^No
Write the valid value
Yes
Write to the register whose value is to
be changed
Write 1 to RCR2.RTCEN
Write operation complete
Note:
The operation of the RTC counter is stopped when RCR2.RTCEN is
cleared to 0. Therefore, using the above method will cause the RTC counter
value to fall behind the actual time by the amount of time that
RCR2.RTCEN was cleared to 0, and the cycle duration for cycle interrupt
generation will be lengthened as well.
Rev.7.00 Oct. 10, 2008 Page 336 of 1074
REJ09B0366-0700