Hitachi SH7750 Hardware Manual page 687

In serial transmission, the SCI operates as described below.
1. The SCI monitors the TDRE flag in SCSSR1. When TDRE is cleared to 0, the SCI recognizes
that data has been written to SCTDR1, and transfers the data from SCTDR1 to SCTSR1.
2. After transferring data from SCTDR1 to SCTSR1, the SCI sets the TDRE flag to 1 and starts
transmission.
The serial transmit data is sent from the TxD pin in the following order.
a. Start bit: One 0-bit is output.
b. Transmit data: 8-bit or 7-bit data is output in LSB-first order.
c. Multiprocessor bit: One multiprocessor bit (MPBT value) is output.
d. Stop bit(s): One or two 1-bits (stop bits) are output.
e. Mark state: 1 is output continuously until the start bit that starts the next transmission is
sent.
3. The SCI checks the TDRE flag at the timing for sending the stop bit. If the TDRE flag is set to
1, the TEND flag in SCSSR1 is set to 1, the stop bit is sent, and then the line goes to the mark
state in which 1 is output. If the TEIE bit in SCSCR1 is set to 1 at this time, a transmit-end
interrupt (TEI) request is generated.
4. The SCI monitors the TDRE flag. When TDRE is cleared to 0, the SCI recognizes that data
has been written to SCTDR1, and transfers the data from SCTDR1 to SCTSR1.
5. After transferring data from SCTDR1 to SCTSR1, the SCI sets the TDRE flag to 1 and starts
transmitting. If the transmit-data-empty interrupt enable bit (TIE bit) in SCSCR1 is set to 1 at
this time, a transmit-data-empty interrupt (TXI) request is generated.
The order of transmission is the same as in step 2.
Figure 15.14 shows an example of SCI operation for transmission using a multiprocessor format.
Rev. 6.0, 07/02, page 637 of 986