M38047FEHKP datasheet(162/387 Pages) RENESAS

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2-38

APPLICATION

2.3 Timer

Rev.1.00 Jan 14, 2005

REJ09B0212-0100Z

3804 Group (Spec.H)

(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 P55/CNTR1 pin with the timer.

•A reference value

Specifications: •The pulse is input to the P55/CNTR1 pin and counted by the timer Y.

•The clock f(XIN) = 8 MHz is dividing by the timer 1, and the interrupt request occurs

at about 2 ms intervals.

•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 count value.

Figure 2.3.22 shows the judgment method of valid/invalid of input pulses; Figure 2.3.23 shows the

relevant registers setting; Figure 2.3.24 shows the control procedure.

Fig. 2.3.22 Judgment method of valid/invalid of input pulses

Input pulse

2 ms

71.4

µs

= 28 counts

• • • • •

71.4

µs or more

(less than 14 kHz)

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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