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7540 Group User
’
s Manual
2-32
APPLICATION
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(X
IN
)/16 (f(X
IN
) = 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(X
IN
) = 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
7
5
4
0
G
r
o
u
p
P
0
0
/
C
N
T
R
1
Ringing pulse
detection circuit
Telephone line
Fig. 2.2.24 Operation timing when ringing pulse is input
I
n
0
0
/
p
u
C
t
s
N
i
g
T
n
R
1
a
l
p
t
o
i
n
P
T
i
m
e
r
A
v
a
l
u
e
T
i
n
r
i
t
m
e
q
e
r
r
u
r
u
e
A
p
s
t
e
t
C
n
r
e
N
t
e
q
T
r
u
R
1
u
p
e
s
i
r
t
t
“
H
”
w
i
d
t
h
m
e
a
s
u
r
e
m
e
n
t
e
n
d
4
i
n
o
t
t
o
e
c
r
u
2
r
r
3
u
p
t
s
c
12 to 43
interrupts
occur
1
o
r
u
u
r
p
5
e
9
p
r
s
i
o
d
2
i
n
o
0
t
c
e
c
t
r
t
(1.0 s to 3.0 s)
Ringing duration
(200 ms to 1.2 s)
No ringing
duration
(600 ms to 2.2 s)
G
W
h
e
n
a
n
o
r
m
a
l
-
r
a
n
g
e
r
i
n
g
i
n
g
p
u
l
s
e
i
s
i
n
p
u
t
R
e
l
o
a
d
Reload
“
L
”
width measurement end