MITSUBISHI MICROCOMPUTERS
3827 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
(1) Clock Synchronous Serial I/O Mode
SERIAL I/O
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.
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.
Data bus
Serial I/O1 control register
Address 001A16
Address 001816
Receive buffer register
Receive buffer full flag (RBF)
Receive shift register
Receive interrupt request (RI)
P44/RXD
Shift clock
Clock control circuit
P46/SCLK
Serial I/O1
clock selection bit
Frequency division ratio 1/(n+1)
BRG count source selection bit
f(XIN
)
Baud rate generator
Address 001C16
1/4
(f(XCIN) in low-speed mode)
1/4
Clock control circuit
Falling-edge detector
P47/SRDY1
F/F
Transmit shift register shift completion flag (TSC)
Shift clock
Transmit shift register
Transmit buffer register
Transmit interrupt source selection bit
P45/TXD
Transmit interrupt request (TI)
Transmit buffer empty flag (TBE)
Serial I/O1 status register
Address 001916
Address 001816
Data bus
Fig. 21 Block diagram of clock synchronous serial I/O1
Transfer shift clock
(1/2 to 1/2048 of the internal
clock, or an external clock)
D0
D0
D1
D1
D2
D2
D3
D3
D4
D4
D5
D5
D6
D6
D7
D7
Serial output TXD
Serial input RXD
Receive enable signal SRDY1
Write signal to receive/transmit
buffer register (address 001816)
RBF = 1
TSC = 1
TBE = 0
TBE = 1
TSC = 0
Overrun error (OE)
detection
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 TXD pin.
3 : The receive interrupt (RI) is set when the receive buffer full flag (RBF) becomes “1” .
Fig. 22 Operation of clock synchronous serial I/O1 function
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MITSUBISHI [ Mitsubishi Group ]
