Hitachi SH7095 Hardware User Manual page 360

In transmitting serial data, the SCI operates as follows:
1. The SCI monitors the TDRE bit in the SSR. When TDRE is cleared to 0, the SCI recognizes
that the transmit data register (TDR) contains new data, and loads this data from the TDR into
the transmit shift register (TSR).
2. After loading the data from the TDR into the TSR, the SCI sets the TDRE bit to 1 and starts
transmitting. If the transmit-data-empty interrupt enable bit (TIE) is set to 1 in the SCR, the
SCI requests a transmit-data-empty interrupt (TXI) at this time.
Serial transmit data is transmitted in the following order from the TxD pin:
a. Start bit: one 0 bit is output.
b. Transmit data: seven or eight bits of data are output, LSB first.
c. Parity bit or multiprocessor bit: one parity bit (even or odd parity) or one multiprocessor
bit is output. Formats in which neither a parity bit nor a multiprocessor bit is output can
also be selected.
d. Stop bit: one or two 1 bits (stop bits) are output.
e. Marking: output of 1 bits continues until the start bit of the next transmit data.
3. The SCI checks the TDRE bit when it outputs the stop bit. If TDRE is 0, the SCI loads new
data from the TDR into the TSR, outputs the stop bit, then begins serial transmission of the
next frame. If TDRE is 1, the SCI sets the TEND bit to 1 in the SSR, outputs the stop bit, then
continues output of 1 bits (marking). If the transmit-end interrupt enable bit (TEIE) in the
SCR is set to 1, a transmit-end interrupt (TEI) is requested.
Figure 13.6 shows an example of SCI transmit operation in the asynchronous mode.
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