HD64F3694HV Datasheet, PDF (222/452 Pages) Renesas Technology Corp – Hardware Manual Renesas 16-Bit Single-Chip Microcomputer H8 Family/H8/300H Tiny Series

Section 14 Serial Communication Interface 3 (SCI3)
14.3.1 Receive Shift Register (RSR)
RSR is a shift register that is used to receive serial data input from the RxD pin and convert it into
parallel data. When one byte of data has been received, it is transferred to RDR automatically.
RSR cannot be directly accessed by the CPU.
14.3.2 Receive Data Register (RDR)
RDR is an 8-bit register that stores received data. When the SCI3 has received one byte of serial
data, it transfers the received serial data from RSR to RDR, where it is stored. After this, RSR is
receive-enabled. As RSR and RDR function as a double buffer in this way, continuous receive
operations are possible. After confirming that the RDRF bit in SSR is set to 1, read RDR only
once. RDR cannot be written to by the CPU. RDR is initialized to H'00.
14.3.3 Transmit Shift Register (TSR)
TSR is a shift register that transmits serial data. To perform serial data transmission, the SCI3 first
transfers transmit data from TDR to TSR automatically, then sends the data that starts from the
LSB to the TXD pin. TSR cannot be directly accessed by the CPU.
14.3.4 Transmit Data Register (TDR)
TDR is an 8-bit register that stores data for transmission. When the SCI3 detects that TSR is
empty, it transfers the transmit data written in TDR to TSR and starts transmission. The double-
buffered structure of TDR and TSR enables continuous serial transmission. If the next transmit
data has already been written to TDR during transmission of one-frame data, the SCI3 transfers
the written data to TSR to continue transmission. To achieve reliable serial transmission, write
transmit data to TDR only once after confirming that the TDRE bit in SSR is set to 1. TDR is
initialized to H'FF.
Rev.5.00 Nov. 02, 2005 Page 192 of 418
REJ09B0028-0500