R8CSLASH20 datasheet(141/501 Pages) RENESAS

141 / 501 page

R8C/20 Group, R8C/21 Group

14. Timers

Rev.2.00 Aug 27, 2008

Page 125 of 458

REJ09B0250-0200

14.1.1.1

Timer Write Control during Count Operation

Timer RA has a prescaler and a timer (which counts the prescaler underflows). The prescaler and timer each

consist of a reload register and a counter. When writing to the prescaler or timer, values are written to both the

reload register and counter.

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, if the prescaler or timer is written to when count

operation is in progress, the counter value is not updated immediately after the WRITE instruction is executed.

Figure 14.6 shows an Operating Example of Timer RA when Counter Value is Rewritten during Count

Operation.

Figure 14.6

Operating Example of Timer RA when Counter Value is Rewritten during Count

Operation

Count source

Reloads register of

timer RA prescaler

IR bit in TRAIC

Counter of

timer RA prescaler

Reloads register of

timer RA

Counter of timer RA

Set 01h to the TRAPRE register and 25h to

the TRA register by a program.

After writing, the reload register is

written to at the first count source.

Reload at

second count

source

Reload at

underflow

After writing, the reload register is

written to at the first underflow.

Reload at the second underflow

The IR bit remains unchanged until underflow is

generated by a new value.

05h

04h

01h

00h

01h

00h

01h

00h

01h

00h

06h

New value (01h)

Previous value

New value (25h)

Previous value

03h

24h

02h

25h

The above applies under the following conditions.

Both bits TSTART and TCSTF in the TRACR register are set to 1 (During count).

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