224
Transmit Data Register (TDR)
Bit
7
6
5
4
3
2
1
0
TDR7
TDR6
TDR5
TDR4
TDR3
TDR2
TDR1
TDR0
Initial value
1
1
1
1
1
1
1
1
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
The transmit data register (TDR) is an 8-bit register for holding transmit data.
When SCI3 detects that the transmit shift register (TSR) is empty, it shifts transmit data written in
TDR to TSR and starts serial data transmission. While TSR is transmitting serial data, the next
byte to be transmitted can be written to TDR, realizing continuous transmission.
TDR can be read or written by the CPU at all times.
TDR is initialized to H'FF upon reset or in standby mode, watch mode, subactive mode, or
subsleep mode.
Serial Mode Register (SMR)
Bit
7
6
5
4
3
2
1
0
COM
CHR
PE
PM
STOP
MP
CKS1
CKS0
Initial value
0
0
0
0
0
0
0
0
Read/Write
R/W
R/W
R/W
R/W
R/W
R/W
R/W
R/W
The serial mode register (SMR) is an 8-bit register for setting the serial data communication
format and for selecting the clock source of the baud rate generator. SMR can be read and written
by the CPU at any time.
SMR is initialized to H'00 upon reset or in standby mode, watch mode, subactive mode, or
subsleep mode.
Bit 7—Communication Mode (COM): Bit 7 selects asynchronous mode or synchronous mode as
the serial data communication mode.
Bit 7: COM
Description
0
Asynchronous mode
(initial value)
1
Synchronous mode
Bit 6—Character Length (CHR): Bit 6 selects either 7 bits or 8 bits as the data length in
asynchronous mode. In synchronous mode the data length is always 8 bits regardless of the setting
here.