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R8C/10 Group
Rev.1.20 Jan 27, 2006 page 63 of 180
REJ09B0019-0120
12.1.5 Pulse Period Measurement Mode
In this mode, the timer measures the pulse period of an external signal fed to INT1/CNTR0 pin (See
“Table 12.6 Pulse Period Measurement Mode Specifications”). Figure 12.9 shows the TXMR register
in pulse period measurement mode. Figure 12.10 shows an operation example in pulse period mea-
surement mode.
Item Specification
Count source f1, f2, f8, f32
Count operation • Down-count
• After an active edge of measurement pulse is input, contents in the read-out buffer is
retained in the first underflow of prescaler X. Then the timer X reloads contents in the
reload register in the second underflow of prescaler X and continues counting.
Count start condition Write “1” (count start) to TXS bit in TXMR register
Count stop condition Write “0” (count stop) to TXS bit in TXMR register
Interrupt request • When Timer X underflows or reloads [Timer X interrupt]
generation timing • Rising or falling of CNTR0 input (end of measurement period) [INT1 interrupt]
INT1/CNTR0 pin function
_______
Measurement pulse input
(1)
(INT1 interrupt input)
CNTR0 pin function Programmable I/O port
Read from timer Contents in the read-out buffer can be read by reading TX register. The value retained in
the read-out buffer is released by reading TX register.
Write to timer
Value written to TX register is written to both reload register and counter.
Same applies to
PREX
register.
Select function • INT1/CNTR
0 polarity switching function
Measurement period of input pulse can be selected with R0EDG bit.
NOTES:
1. The period of input pulse must be longer than twice the period of prescaler X. Longer pulse for H width and L width than the
prescaler X period must be input. If shorter pulse than the period is input to the CNTR0 pin, the input may be disabled.
Table 12.6 Pulse Period Measurement Mode Specifications
T
i
m
e
r
X
m
o
d
e
r
e
g
i
s
t
e
r
Symbol Address After reset
TXMR 008B
16
00
16
Bit name
F
u
n
c
t
i
o
nB
i
t
s
y
m
b
o
l
b
7
b
6
b
5
b
4
b
3
b
2
b
1
b
0
0
0
:
T
i
m
e
r
m
o
d
e
o
r
p
u
l
s
e
p
e
r
i
o
d
m
e
a
s
u
r
e
m
e
n
t
m
o
d
e
b1 b0
T
X
M
O
D
1
R
0
E
D
G
T
X
M
O
D
0
I
N
T
1
/
C
N
T
R
0
p
o
l
a
r
i
t
y
s
w
i
t
c
h
i
n
g
b
i
t
(1
)
O
p
e
r
a
t
i
o
n
m
o
d
e
s
e
l
e
c
t
b
i
t
0
,
1
1
0
0
0
RW
R
W
R
W
R
W
T
X
M
O
D
2
TXS
T
X
O
C
N
T
Timer X count
start flag
0 : Stops counting
1 : Starts counting
O
p
e
r
a
t
i
o
n
m
o
d
e
s
e
l
e
c
t
b
i
t
2
1
:
P
u
l
s
e
p
e
r
i
o
d
m
e
a
s
u
r
e
m
e
n
t
m
o
d
e
S
e
t
t
o
“
0
”
i
n
p
u
l
s
e
p
e
r
i
o
d
m
e
a
s
u
r
e
m
e
n
t
m
o
d
e
T
X
E
D
G
(2
)
T
X
U
N
D
(2
)
T
i
m
e
r
X
u
n
d
e
r
f
l
o
w
f
l
a
g
0
:
N
o
u
n
d
e
r
f
l
o
w
1
:
U
n
d
e
r
f
l
o
w
f
o
u
n
d
0
:
N
o
a
c
t
i
v
e
e
d
g
e
1
:
A
c
t
i
v
e
e
d
g
e
f
o
u
n
d
Active edge
j
udgment flag
N
O
T
E
S:
1
.
T
h
e
I
R
b
i
t
i
n
t
h
e
I
N
T
1
I
C
r
e
g
i
s
t
e
r
m
a
y
b
e
s
e
t
t
o
“
1
”
(
i
n
t
e
r
r
u
p
t
r
e
q
u
e
s
t
e
d
)
w
h
e
n
t
h
e
R
0
E
D
G
b
i
t
i
s
r
e
w
r
i
t
t
e
n
.
R
e
f
e
r
t
o
t
h
e
p
a
r
a
g
r
a
p
h
1
9
.
2
.
5
“
C
h
a
n
g
i
n
g
I
n
t
e
r
r
u
p
t
F
a
c
t
o
r
”
i
n
t
h
e
U
s
a
g
e
N
o
t
e
s
R
e
f
e
r
e
n
c
e
B
o
o
k
.
2
.
T
h
i
s
b
i
t
i
s
s
e
t
t
o
“
0
”
b
y
w
r
i
t
i
n
g
“
0
”
i
n
a
p
r
o
g
r
a
m
.
(
I
t
r
e
m
a
i
n
s
u
n
c
h
a
n
g
e
d
e
v
e
n
i
f
w
r
i
t
i
n
g
“
1
”
)
R
W
R
W
R
W
R
W
R
W
[CNTR
0
]
0: Measures a measurement pulse from one
rising edge to the next rising edge
1: Measures a measurement pulse from one
falling edge to the next falling edge
[INT1]
0: Rising edge
1: Falling edge
Figure 12.9 TXMR Register in Pulse Period Measurement Mode
12.1 Timer (Timer X)
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