SH7101 datasheet(340/560 Pages) RENESAS

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Section 10 Serial Communication Interface (SCI)

Rev.1.00 Sep. 18, 2008 Page 306 of 522

REJ09B0069-0100

10.4.5

Data Transmission (Asynchronous Mode)

Figure 10.6 shows an example of the operation for transmission in asynchronous mode. In

transmission, the SCI operates as described below.

1. The SCI monitors the TDRE flag in SSR, and if is cleared to 0, recognizes that data has been

written to TDR, and transfers the data from TDR to TSR.

2. After transferring data from TDR to TSR, the SCI sets the TDRE flag to 1 and starts

transmission. If the TIE bit is set to 1 at this time, a transmit data empty interrupt request

(TXI) is generated. Because the TXI interrupt routine writes the next transmit data to TDR

before transmission of the current transmit data has finished, continuous transmission can be

enabled.

3. Data is sent from the TxD pin in the following order: start bit, transmit data, parity bit, or

multiprocessor bit (may be omitted depending on the format), and stop bit.

4. The SCI checks the TDRE flag at the timing for sending the stop bit.

5. If the TDRE flag is 0, the data is transferred from TDR to TSR, the stop bit is sent, and then

serial transmission of the next frame is started.

6. If the TDRE flag is 1, the TEND flag in SSR is set to 1, the stop bit is sent, and then the “mark

state” is entered in which 1 is output. If the TEIE bit in SCR is set to 1 at this time, a TEI

interrupt request is generated.

Figure 10.7 shows a sample flowchart for transmission in asynchronous mode.

TDRE

TEND

One frame

0/1

Data

Start

bit

Parity

bit

Stop

bit

Start

bit

Data

Parity

bit

Stop

bit

Data written to TDR

and TDRE flag cleared

to 0 in TXI interrupt

processing routine

TEI interrupt

request

generated

Idle state

(mark state)

TxD

TXI interrupt

request

generated

TXI interrupt

request

generated

Figure 10.6 Example of Operation in Transmission in Asynchronous Mode

(Example with 8-Bit Data, Parity, One Stop Bit)

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