7540 datasheet(132/366 Pages) RENESAS

132 / 366 page

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REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

APPLICATION

7540 Group

2.4 Timer X

(3) Application example of event counter mode

Outline: Pulses generated corresponding to the water flow rate are counted for a fixed period

(100 ms), and the water flow rate during this period is calculated.

Specifications: Pulses generated corresponding to the water flow rate are input to the P14/CNTR0

pin and counted using timer X.

The contents of timer X are read in the timer Y interrupt processing routine generated

after 100 ms from the start of counting pulses, and the water flow rate during 100

ms is calculated.

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

Figure 2.4.20 shows an example of peripheral circuit, Figure 2.4.21 shows the method of measuring

water flow rate, and Figure 2.4.21 shows an example of control procedure.

Fig. 2.4.20 Example of peripheral circuit

7540 Group

P14/CNTR0

Water flow rate sensor

Water

flow

Blades rotate in proportion to

water flow and generate pulses.

The faster the water flow,

the shorter the pulse period.

Fig. 2.4.21 Method of measuring water flow rate

CNTR0 pin input

Timer Y interrupt request bit

100 ms

Timer X counting (Note)

Note: Counting rising edges.

• Flow rate during 100 ms = (FF16–read value of timer X) ✕ flow rate per pulse

Timer Y interrupt processing routine

• Timer X, timer Y stop counting.

• Timer X is read out.

Timer X, timer Y

start counting.

7540 Datasheet(PDF) 132 Page - Renesas Technology Corp