Toshiba TLCS-900/H1 Series Data Book page 311

(2) Writing timer data
When there is carry on the way of write operation, expecting data can not be wrote exactly.
Therefore, in order to write in data exactly please follow the below way.
① Resetting a divider
In RTC inside, there are 15-stage dividers, which generates 1Hz clock from 32,768KHz. Carry of a timer
is not done for one second when reset this divider. So write in data at this interval.
START
PAGER<PA0>='0'
Select PAGE0
RESTR<RSTTMR>='1'
Divider reset
Write the timer data
END
Figure 3.13(4) Flowchart of data write
92CH21- 307
TMP92CH21
(Note)
This period is within
0.5 second.