SH7708 datasheet(389/633 Pages) RENESAS

389 / 633 page

371

In transmitting serial data, the SCI operates as follows:

1. The SCI monitors the TDRE bit in SCSSR. When TDRE is cleared to 0, the SCI recognizes

that the transmit data register (SCTDR) contains new data, and loads this data from SCTDR

into the transmit shift register (SCTSR).

2. After loading the data from SCTDR into SCTSR, 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 SCSCR, 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 SCTDR into SCTSR, 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 SCSSR, outputs the stop bit, then

continues output of 1 bits (marking). If the transmit-end interrupt enable bit (TEIE) in SCSCR

is set to 1, a transmit-end interrupt (TEI) is requested.

SH7708 Datasheet(PDF) 389 Page - Renesas Technology Corp