Receive Shift Register (Rsr); Receive Data Register (Rdr); Transmit Data Register (Tdr) - Renesas H8SX/1650 Hardware Manual

Section 13 Serial Communication Interface (SCI)
13.3.1

Receive Shift Register (RSR)

RSR is a shift register which is used to receive serial data input from the RxD pin and converts it
into parallel data. When one frame of data has been received, it is transferred to RDR
automatically. RSR cannot be directly accessed by the CPU.
13.3.2

Receive Data Register (RDR)

RDR is an 8-bit register that stores receive data. When the SCI has received one frame of serial
data, it transfers the received serial data from RSR to RDR where it is stored. This allows RSR to
receive the next data. Since RSR and RDR function as a double buffer in this way, continuous
receive operations can be performed. After confirming that the RDRF bit in SSR is set to 1, read
RDR only once. RDR cannot be written to by the CPU.
Bit 7
Bit Name
Initial Value 0
R/W R
13.3.3

Transmit Data Register (TDR)

TDR is an 8-bit register that stores transmit data. When the SCI detects that TSR is empty, it
transfers the transmit data written in TDR to TSR and starts transmission. The double-buffered
structures of TDR and TSR enables continuous serial transmission. If the next transmit data has
already been written to TDR when one frame of data is transmitted, the SCI transfers the written
data to TSR to continue transmission. Although TDR can be read from or written to by the CPU at
all times, to achieve reliable serial transmission, write transmit data to TDR for only once after
confirming that the TDRE bit in SSR is set to 1.
Bit 7
Bit Name
Initial Value 1
R/W R/W
Rev.2.00 Jun. 28, 2007 Page 454 of 666
REJ09B0311-0200
6 5
0 0
R R
6 5
1 1
R/W R/W
4 3
0 0
R R
4 3
1 1
R/W R/W
2 1
0 0
R R
2 1
1 1
R/W R/W
0
0
R
0
1
R/W