25
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
MITSUBISHI MICROCOMPUTERS
3827 Group
SERIAL I/O
Serial I/O1
Serial I/O1 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/O1 can be selected by setting the
mode selection bit of the serial I/O1 control register to “1”.
For clock synchronous serial I/O1, 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 registers.
Fig. 21 Block diagram of clock synchronous serial I/O1
Fig. 22 Operation of clock synchronous serial I/O1 function
P4
6
/S
CLK
P4
7
/S
RDY1
P4
4
/R
X
D
P4
5
/T
X
D
f(X
IN
)
1/4
1/4
F/F
Serial I/O1 status register
Serial I/O1 control register
Receive buffer register
Address 0018
16
Receive shift register
Receive buffer full flag (RBF)
Receive interrupt request (RI)
Clock control circuit
Shift clock
Serial I/O1
clock selection bit
Frequency division ratio 1/(n+1)
Baud rate generator
Address 001C
16
BRG count source selection bit
Clock control circuit
Falling-edge detector
Data bus
Address 0018
16
Shift clock
Transmit shift register shift completion flag (TSC)
Transmit interrupt source selection bit
Transmit buffer empty flag (TBE)
Address 0019
16
Transmit interrupt request (TI)
Data bus
Address 001A
16
Transmit buffer register
Transmit shift register
(f(X
CIN
) in low-speed mode)
Receive enable signal S
RDY1
D
7
D
0
D
1
D
2
D
3
D
4
D
5
D
6
RBF = 1
TSC = 1
Overrun error (OE)
detection
TBE = 0
TBE = 1
TSC = 0
Transfer shift clock
(1/2 to 1/2048 of the internal
clock, or an external clock)
Serial output T
X
D
Serial input R
X
D
Write signal to receive/transmit
buffer register (address 0018
16
)
Notes 1 :
The transmit interrupt (TI) can be selected to occur either when the transmit buffer register has emptied (TBE=1)
or after the transmit shift operation has ended (TSC=1), by setting the transmit interrupt source selection bit (TIC) of the
serial I/O1 control register.
2 :
If data is written to the transmit buffer register when TSC=0, the transmit clock is generated continuously and serial data is
output continuously from the T
X
D pin.
3 :
The receive interrupt (RI) is set when the receive buffer full flag (RBF) becomes “1” .
D
7
D
0
D
1
D
2
D
3
D
4
D
5
D
6