Datasheet

Section 15 Serial Communication Interface (SCI, IrDA)
Rev. 3.00 Mar 17, 2006 page 666 of 926
REJ09B0283-0300
15.3.3 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 enable continuous serial transmission. If the next transmit data has
already been written to TDR during serial transmission, the SCI transfers the written data to TSR
to continue transmission. Although TDR can be read 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.
15.3.4 Transmit Shift Register (TSR)
TSR is a shift register that transmits serial data. To perform serial data transmission, the SCI first
transfers transmit data from TDR to TSR, then sends the data to the TxD pin starting. TSR cannot
be directly accessed by the CPU.
15.3.5 Serial Mode Register (SMR)
SMR is used to set the SCI’s serial transfer format and select the on-chip baud rate generator clock
source.
Some bit functions of SMR differ in normal serial communication interface mode and Smart Card
interface mode.