SH7108 Datasheet, PDF (361/560 Pages) Renesas Technology Corp – 32-Bit RISC Microcomputer

Section 10 Serial Communication Interface (SCI)
10.8 Usage Notes
10.8.1 TDR Write and TDRE Flag
The TDRE bit in the serial status register (SSR) is a status flag indicating transferring of transmit
data from TDR into TSR. The SCI sets the TDRE bit to 1 when it transfers data from TDR to
TSR.
Data can be written to TDR regardless of the TDRE bit status.
If new data is written in TDR when the TDRE bit is 0, however, the old data stored in TDR will be
lost because the data has not yet been transferred to TSR. Before writing transmit data to TDR, be
sure to check that the TDRE bit is set to 1.
10.8.2 Module Standby Mode Setting
SCI operation can be disabled or enabled using the module standby control register. The initial
setting is for SCI operation to be halted. Register access is enabled by clearing module standby
mode. For details, refer to section 18, Power-Down Modes.
10.8.3 Break Detection and Processing (Asynchronous Mode Only)
When framing error detection is performed, a break can be detected by reading the RxD pin value
directly. In a break, the input from the RxD pin becomes all 0s, and so the FER flag is set, and the
PER flag may also be set. Note that, since the SCI continues the receive operation after receiving
a break, even if the FER flag is cleared to 0, it will be set to 1 again.
10.8.4 Sending Break Signal (Asynchronous Mode Only)
The TxD pin becomes of the I/O port general I/O pin with the I/O direction and level determined
by the port data register (DR) and the port I/O register (IOR) of the pin function controller (PFC).
These conditions allow break signals to be sent.
The DR value is substituted for the marking status until the PFC is set. Consequently, the output
port is set to initially output a 1.
To send a break in serial transmission, first clear the DR to 0, then establish the TxD pin as an
output port using the PFC.
When the TE bit is cleared to 0, the transmission section is initialized regardless of the present
transmission status.
Rev.1.00 Sep. 18, 2008 Page 327 of 522
REJ09B0069-0100