38K2 datasheet(182/358 Pages) RENESAS

182 / 358 page

2.3 Timer

Rev.2.00

Oct 15, 2006

page 33 of 112

38K2 Group

REJ09B0338-0200

APPLICATION

(4)

Timer application example 3: Frequency measurement

Outline: The following two values are compared to judge whether the frequency is within a valid

range.

•A value by counting pulses input to P51/CNTR0 pin with the timer.

•A reference value

Specifications: •The pulse is input to the P51/CNTR0 pin and counted by the timer X.

•A count value is read out at about 2 ms intervals, the timer 1 interrupt interval.

When the count value is 28 to 40, it is judged that the input pulse is valid.

•Because the timer is a down-counter, the count value is compared with 227 to 215

(Note).

Note: 227 to 215 = {255 (initial value of counter) – 28} to {255 – 40}; 28 to 40 means the number

of valid value.

Figure 2.3.17 shows the judgment method of valid/invalid of input pulses; Figure 2.3.18 shows the

related registers setting; Figure 2.3.19 shows the control procedure.

Fig. 2.3.17 Judgment method of valid/invalid of input pulses

Input pulse

2 ms

71.4

µs

= 28 counts

......

71.4

µs or more

(14 kHz or less)

71.4

µs

(14 kHz)

µs

(20 kHz)

µs or less

(20 kHz or more)

Invalid

Valid

Invalid

2 ms

µs

= 40 counts

......

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