4501 datasheet(199/212 Pages) RENESAS

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3.3 List of precautions

3-30

Rev.2.01

Feb 07, 2005

4501 Group

APPENDIX

REJ09B0192-0201

3.3.5 Notes on timer

(1)

Prescaler

Stop the prescaler operation to change its frequency dividing ratio.

(2)

Count source

Stop timer 1 or 2 counting to change its count source.

(3)

Reading the count values

Stop timer 1 or 2 counting and then execute the TAB1 or TAB2 instruction to read its data.

(4)

Writing to the timer

Stop timer 1 or 2 counting and then execute the T1AB or T2AB instruction to write its data.

(5)

Writing to reload register R1

When writing data to reload register R1 while timer 1 is operating, avoid a timing when timer 1

underflow.

(6)

Timer 1 and timer 2 count start timing and count time when operation starts

Count starts from the first rising edge of the count source (2) after timer 1 and timer 2 operations start (1).

Time to first underflow (3) is shorter (for up to 1 period of the count source) than time among next

underflow (4) by the timing to start the timer and count source operations after count starts.

When selecting CNTR input as the count source of timer 2, timer 2 operates synchronizing with the

falling edge of CNTR input.

Parameter

Timer external input period

(“H” and “L” pulse width)

Condition

High-speed mode

Middle-speed mode

Low-speed mode

Default mode

Min.

3/f(XIN)

6/f(XIN)

12/f(XIN)

24/f(XIN)

Unit

Typ.

Max.

Rating value

(7)

Watchdog timer

• The watchdog timer function is valid after system is released from reset. When not using the

watchdog timer function, execute the DWDT instruction and the WRST instruction continuously, and

clear the WEF flag to “0” to stop the watchdog timer function.

• The watchdog timer function is valid after system is returned from the RAM back-up. When not

using the watchdog timer function, execute the DWDT instruction and the WRST instruction continu-

ously every system is returned from the RAM back-up, and stop the watchdog timer function.

(8) Pulse width input to CNTR pin

Table 3.3.2 shows the recommended operating condition of pulse width input to CNTR pin.

Table 3.3.2 Recommended operating condition of pulse width input to CNTR pin

Fig. 3.3.4

Timer count start timing and count time when operation starts (T1, T2)

(1) Timer

Count Source

Timer Value

Timer Underflow

Signal

032

103

Count Source

(CNTR input)

(2)

(3)

(4)

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