RSR cannot be read or written directly by the CPU.
10.2.2 Receive data register (RDR)
RDR is an 8-bit register that stores received serial data.
When reception of one byte of data is finished, the received data is transferred from RSR to RDR,
and the receive operation is completed. RSR is then able to receive data. RSR and RDR are
double-buffered, allowing consecutive receive operations.
RDR is a read-only register, and cannot be written by the CPU.
RDR is initialized to H'00 upon reset, and in standby, module standby or watch mode.
10.2.3 Transmit shift register (TSR)
TSR is a register used to transmit serial data. Transmit data is first transferred from TDR to TSR,
and serial data transmission is carried out by sending the data to the TXD
3x
pin in order, starting
from the LSB (bit 0). When one byte of data is transmitted, the next byte of transmit data is
transferred to TDR, and transmission started, automatically. Data transfer from TDR to TSR is not
performed if no data has been written to TDR (if bit TDRE is set to 1 in the serial status register
(SSR)).
TSR cannot be read or written directly by the CPU.
Bit
Read/Write
7
—
6
—
5
—
4
—
3
—
0
—
2
—
1
—
Bit
Initial value
Read/Write
7
RDR7
0
R
6
RDR6
0
R
5
RDR5
0
R
4
RDR4
0
R
3
RDR3
0
R
0
RDR0
0
R
2
RDR2
0
R
1
RDR1
0
R
253