7540 datasheet(108/366 Pages) RENESAS

108 / 366 page

2-32

REJ09B0018-0200Z

Rev.2.00

Jun 21, 2004

APPLICATION

7540 Group

2.2 Timer A

(3) Application example of pulse width HL continuously measurement mode

Outline: A telephone ringing (calling) pulse* is detected by using the pulse width HL continuously

measurement mode.

* Signal which is sent by turning on/off (make/break) the telephone line.

Each country has a different standard. In this case, Japanese domestic standard is adopted as an

example.

Specifications: Whether a telephone call exists or not is judged by measuring a pulse width output

from the ringing signal detection circuit.

f(XIN)/16 (f(XIN) = 6.4 MHz) is used as the count source, and “H” and “L” pulse width

of the ringing pulse are measured by using the pulse width HL continuously measurement

mode. When the following conditions are satisfied, it is recognized as a normal

value. When the following conditions are not satisfied, it is recognized as an unusual

value.

200 ms

≤ “H” pulse width of ringing pulse < 1.2 s

600 ms

≤ “L” pulse width of ringing pulse < 2.2 s

1.0 s

≤ one period (“H” pulse width + “L” pulse width) < 3.0 s

Operation clock: f(XIN) = 6.4 MHz, high-speed mode

Figure 2.2.23 shows an example of a peripheral circuit, and Figure 2.2.24 shows an operation timing

when a ringing pulse is input. Figures 2.2.25 and 2.2.26 show an example of control procedure.

Fig. 2.2.23 Example of peripheral circuit

7540 Group

P00/CNTR1

Ringing pulse

detection circuit

Telephone line

Fig. 2.2.24 Operation timing when ringing pulse is input

Input signal to

P00/CNTR1 pin

Timer A value

Timer A

interrupt

request

CNTR1

interrupt

request

“H” width measurement end

4 to 23

interrupts

occur

12 to 43

interrupts

occur

1 period

20 to 59

interrupts

occur

(1.0 s to 3.0 s)

Ringing duration

(200 ms to 1.2 s)

No ringing

duration

(600 ms to 2.2 s)

q When a normal-range ringing pulse is input

Reload

“L” width measurement end

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