7540 datasheet(104/366 Pages) RENESAS

104 / 366 page

2-28

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

APPLICATION

7540 Group

2.2 Timer A

(3) Application example of event counter mode

Outline: The frequency of the pulse which is input to the P00/CNTR1 pin (“H” active) is measured by

the number of events in a certain period.

Specifications: The count source of timer A is input from the P00/CNTR1 pin, and the timer A starts

counting the count source. Clock (f(XIN) = 8 MHz) is divided by timer X to detect 1

ms. The frequency of the pulse input to the P00/CNTR1 pin is calculated by the

number of events counted within 1 ms.

Operation clock: f(XIN) = 8 MHz, high-speed mode

Figure 2.2.19 shows an example of measurement method of frequency, and Figure 2.2.20 shows an

example of control procedure.

Fig. 2.2.19 Example of measurement method of frequency

Notes 1: Counted at falling edge.

2: Frequency of pulse input from P00/CNTR1 pin:

Timer X interrupt processing routine

• Timer A, Timer X count stop

• Timer A read

• Timer A, Timer X set again

• Timer A, Timer X count restart

P00/CNTR1 pin input

Timer X interrupt request bit

1ms

Counted by Timer A (Note 1)

X times (Note 2)

Timer A, Timer X

count start

kHz

X times

1ms

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