Rev.2.02
Mar 31, 2009
REJ03B0202-0202
7549 Group
(2) Asynchronous Serial I/O (UART) Mode
Clock asynchronous serial I/O mode (UART) can be selected by
clearing the serial I/O mode selection bit of the serial I/O control
register to “0”.
Eight serial data transfer formats can be selected, and the transfer
formats used by a transmitter and receiver must be identical.
The transmit and receive shift registers each have a buffer, but
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 register, and receive data is read
from the receive buffer register.
The transmit buffer register can also hold the next data to be
transmitted, and the receive buffer register can hold a character
while the next character is being received.
Fig 47. Block diagram of UART serial I/O
Fig 48. Operation of UART serial I/O function
1/4
OE
PE FE
1/16
Data bus
Receive buffer register
Address 001816
Receive shift register
Receive buffer full flag (RBF)
Receive interrupt request (RI)
Baud rate generator
Frequency division ratio 1/(n+1)
Address 001C16
ST/SP/PA generator
Transmit buffer register
Transmit shift register
Address 001816
Transmit shift completion flag (TSC)
Transmit buffer empty flag (TBE)
Transmit interrupt request (TI)
Address 001916
ST detector
SP detector
UART control register
Address 001B16
Character length selection bit
Address 001A16
BRG count source selection bit
Transmit interrupt source selection bit
Serial I/O1 synchronous clock selection bit
Clock control circuit
Character length selection bit
7 bits
8 bits
Serial I/O1 status register
Serial I/O 1 control register
P06/SCLK
P04/RXD
P05/TXD
φSOURCE
TSC=0
TBE=1
RBF=0
TBE=0
RBF=1
TBE=1
TSC=1*
ST
D0
D1
SP
D0
D1
ST
SP
Transmit or receive clock
Transmit buffer
write signal
Serial output TXD
Receive buffer
read signal
Serial input RXD
* 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 (s)
Notes 1: Error flag detection occurs at the same time that the RBF flag becomes “1” (at 1st stop bit, during reception).
2: As the transmit interrupt (TI), when either the TBE or TSC flag becomes “1”, can be selected to occur depending on the setting of the transmit
interrupt source selection bit (TIC) of the serial I/O1 control register.
3: The receive interrupt (RI) is set when the RBF flag becomes “1”.
4: After data is written to the transmit buffer when TSC=1, 0.5 to 1.5 cycles of the data shift cycle is necessary until changing to TSC=0.
ST
D0
D1
SP
D0
D1
ST
SP