Datasheet

Section 15 Serial Communication Interface (SCI)
Rev. 6.00 Mar. 18, 2010 Page 552 of 982
REJ09B0054-0600
• Serial status register (SSR)
• Smart card mode register (SCMR)
• Bit rate register (BRR)
• Serial expansion mode register (SEMR0)*
Note: * This register is in the channel 0 of the H8S/2239 Group only.
15.3.1 Receive Shift Register (RSR)
RSR is a shift register that is used to receive serial data input to 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.
15.3.2 Receive Data Register (RDR)
RDR is an 8-bit register that stores received data. When the SCI 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 by a reset, in standby mode, watch mode, subactive mode, subsleep
mode, or module stop mode.
15.3.3 Transmit Data Register (TDR)
TDR is an 8-bit register that stores data for transmission. When the SCI 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 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 only once after confirming that the
TDRE bit in SSR is set to 1.
TDR is initialized to H'FF by a reset, in standby mode, watch mode, subactive mode, subsleep
mode or module stop mode.