29
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
3822 Group
MITSUBISHI MICROCOMPUTERS
SERIAL I/O
Serial I/O can be used as either clock synchronous or asynchro-
nous (UART) serial I/O. A dedicated timer (baud rate generator) is
also provided for baud rate generation.
(1) Clock Synchronous Serial I/O Mode
Clock synchronous serial I/O can be selected by setting the mode
selection bit of the serial I/O control register to “1”.
For clock synchronous serial I/O, the transmitter and the receiver
must use the same clock. If an internal clock is used, transfer is
started by a write signal to the transmit/receive buffer register.
Fig. 25 Block diagram of clock synchronous serial I/O
Fig. 26 Operation of clock synchronous serial I/O function
4
6
/
C
L
4
7
/
R
D
Y
1
4
4
/
X
4
5
/
X
I
N
1/4
1
/
4
/
Serial I/O status register
S
e
r
i
a
l
I
/
O
c
o
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t
r
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r
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g
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6
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p
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q
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s
t
Clock control circuit
t c
oc
er
a
/
clock selection bit
Frequency division ratio 1/(n+1)
Baud rate generator
r
e
s
s
0
0
1
1
6
count source se
ect
on
t
C
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c
k
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c
i
r
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u
i
t
Falling-edge detector
ata
us
r
e
s
s
0
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1
8
1
6
t
c
o
c
r
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g
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t
u
er empty
ag
ransm
t
nterrupt request
ransm
t
nterrupt source se
ect
on
t
r
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s
s
0
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1
9
1
6
a
t
a
u
s
r
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s
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0
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1
1
6
Transmit buffer register
T
r
a
n
s
m
i
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s
h
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r
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a
R
D
7
0
1
2
3
4
5
6
= 1
TSC = 1
=
0
=
1
T
S
C
=
0
rans
er s
t c
oc
(1/2 to 1/2048 of the internal
clock, or an external clock)
e
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)
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(
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(
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)
b
e
c
o
m
e
s
“
1
”
.
7
0
1
2
3
4
5
6
(16 Seiten)
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