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MITSUBISHI MICROCOMPUTERS
38B5 Group
SINGLE-CHIP 8-BIT CMOS MICROCOMPUTER
34
PRELIMINAR
Y
Notice:
This
is not
a final
specification.
Some
parametric
limits
are
subject
to change.
(2) Asynchronous Serial I/O (UART) Mode
The asynchronous serial I/O (UART) mode can be selected by clear-
ing the serial I/O2 mode selection bit (b6) of the serial I/O2 control
register (address 001D16) to “0.” Eight serial data transfer formats
can be selected and the transfer formats used by the transmitter
and receiver must be identical.
The transmit and receive shift registers each have a buffer (the two
buffers have the same address in memory). Since the shift register
cannot be written to or read from directly, transmit data is written to
the transmit buffer, and receive data is read from the receive buffer.
The transmit buffer can also hold the next data to be transmitted,
and the receive buffer can receive 2-byte data continuously.
Fig. 37 Operation of UART Serial I/O2 Function
Fig. 36 Block Diagram of UART Serial I/O2
TSC=0
TBE=1
RBF=0
TBE=0
RBF=1
ST
D0
D1
SP
D0
D1
ST
SP
TBE=1
TSC=1*
ST
D0
D1
SP
D0
D1
ST
SP
Transmit or receive clock
* Generated at 2nd bit in 2-stop
bit mode
1 start bit
7 or 8 data bit
1 or 0 parity bit
1 or 2 stop bit
Serial I/O2 input RXD
Write-in signal to
transmit buffer register
Serial I/O2 output TXD
Read-out signal from receive
buffer register
OE
PE FE
1/16
Transmit buffer register
Clock control circuit
P56/SCLK21
P54/RXD
P55/TXD
P57/SRDY2/SCLK22
“0”
“1”
1/4
“0”
“1”
XIN
1/2
XCIN
“1”
Data bus
Receive buffer register
Address 001F16
Receive shift register
Receive buffer full flag (RBF)
Receive interrupt request (RI)
Baud rate generator
Division ratio 1/(n+1)
Address 001616
ST/SP/PA generator
Data bus
Transmit shift register
Address 001F16
Transmit shift register shift
completion flag (TSC)
Transmit buffer empty flag (TBE)
Transmit interrupt request (TI)
Address 001E16
ST detector
UART control register
Address 001716
Character length selection bit
Address 001D16
BRG count source
selection bit
Transmit interrupt source selection bit
Serial I/O2 synchronous
clock selection bit
Character length selection bit
7 bit
8 bit
Serial I/O2 control register
Serial I/O2 status register
SP detector
Serial I/O2 clock I/O pin
selection bit
Internal system clock selection bit
BRG clock
switch bit