SH7052 datasheet(497/919 Pages) RENESAS

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In transmitting serial data, the SCI operates as follows:

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

the transmit data register (TDR) contains new data, and loads this data from TDR into the

transmit shift register (TSR).

2. After loading the data from TDR into 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 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 TDR into 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 SSR, outputs the stop bit, then

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

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

Figure 14.6 shows an example of SCI transmit operation in asynchronous mode.

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