
Rev.2.40 Jun 14, 2004 page 40 of 56
38C1 Group
Fig. 42 Clock generating circuit block diagram
S
R
Q
XI
N-
XO
U
T
o
s
c
i
l
l
a
t
i
o
n
s
t
o
p
b
i
t
C
P
U
M
B
I
T
5
X
I
N
X
O
U
T
X
C
O
U
T
X
C
I
N
Port Xc switch bit
CPUM BIT4
“
0
”
“
1
”
M
a
i
n
c
l
o
c
k
s
e
l
e
c
t
i
o
n
b
i
t
C
P
U
M
B
I
T
3
On-chip oscillator
1/4
1
/
2
M
a
i
n
c
l
o
c
k
d
i
v
i
s
i
o
n
r
a
t
i
o
s
e
l
e
c
t
i
o
n
b
i
t
C
P
U
M
B
I
T
6
Main clock
selection bit
CPUM BIT3
S
R
Q
Timer 1
S
R
Q
WIT instruction
T
i
m
i
n
g
φ
(
I
n
t
e
r
n
a
l
c
l
o
c
k
)
STP instruction
Interrupt request
Reset
Timer 1 count
source selection bit
T123M BIT 5
Internal system
clock selection bit
CPUM BIT7
Note: When Xc oscillation is selected for internal system clock, set the port Xc switch bit to “1”.
I
n
t
e
r
r
u
p
t
d
i
s
a
b
l
e
f
l
a
g
I
S
T
P
i
n
s
t
r
u
c
t
i
o
n
I
n
t
e
r
n
a
l
s
y
s
t
e
m
c
l
o
c
k
s
e
l
e
c
t
i
o
n
b
i
t
(
N
o
t
e
)
C
P
U
M
B
I
T
7
“0”
“
1
”
“1” “0”
“
1
”
“0”
“0”
“1”
“
0
”
“
1
”
“
0
”
“
1
”
1
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2
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