Rev.1.01
Jan 25, 2005
page 48 of 114
REJ03B0131-0101Z
3804 Group (Spec. H)
(2) Asynchronous Serial I/O (UART) Mode
Clock asynchronous serial I/O mode (UART) can be selected by
clearing the serial I/O3 mode selection bit of the serial I/O3 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 a 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. 42 Block diagram of UART serial I/O3
Fig. 43 Operation of UART serial I/O3
f(XIN)
1/4
OE
PEFE
1/16
Data bus
Receive buffer register 3
Address 003016
Receive shift register 3
Receive buffer full flag (RBF)
Receive interrupt request (RI)
Baud rate generator 3
Frequency division ratio 1/(n+1)
Address 002F16
ST/SP/PA generator
Transmit buffer register 3
Data bus
Transmit shift register 3
Address 003016
Transmit shift completion flag (TSC)
Transmit buffer empty flag (TBE)
Transmit interrupt request (TI)
Address 003116
ST detector
SP detector
UART3 control register
Address 003316
Character length selection bit
Address 003216
BRG count source selection bit
Transmit interrupt source selection bit
Serial I/O3 synchronous clock selection bit
Clock control circuit
Character length selection bit
7 bits
8 bits
Serial I/O3 control register
P36/SCLK3
Serial I/O3 status register
P34/RXD3
P35/TXD3
(f(XCIN) in low-speed mode)
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
Transmit buffer write
signal
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)
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/O3 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 are necessary until changing to TSC=0.
Notes
Serial output TXD3
Serial input RXD3
Receive buffer read
signal