R8C/20 Group, R8C/21 Group 14. Timers
Rev.2.00 Aug 27, 2008 Page 142 of 458
REJ09B0250-0200
14.2.1.1 Timer Write Control during Count Operation
Timer RB has a prescaler and a timer (which counts the prescaler underflows). The prescaler and timer each
consist of a reload register and a counter. In timer mode, the TWRC bit in the TRBMR register can be used to
select whether writing to the prescaler or timer during count operation is performed to both the reload register
and counter or only to the reload register.
However, values are transferred from the reload register to the counter of the prescaler in synchronization with
the count source. In addition, values are transferred from the reload register to the counter of the timer in
synchronization with prescaler underflows. Therefore, even if the TWRC bit is set for writing to both the reload
register and counter, the counter value is not updated immediately after the WRITE instruction is executed. In
addition, if the TWRC bit is set for writing to the reload register only, the synchronization of the writing will be
shifted if the prescaler value changes.
Figure 14.18 shows an Operating Example of Timer RB when Counter Value is Rewritten during Count
Operation.
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