H8SSLASH2218 datasheet(456/750 Pages) RENESAS

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Section 12 Serial Communication Interface

Rev.6.00 Jun. 03, 2008 Page 408 of 698

REJ09B0074-0600

12.4.5

Data Transmission (Asynchronous Mode)

Figure 12.9 shows an example of operation for transmission in asynchronous mode. In

transmission, the SCI operates as described below.

1. The SCI monitors the TDRE flag in SSR. If the flag is cleared to 0, the SCI 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. Continuous transmission is possible because the TXI interrupt routine writes next

transmit data to TDR before transmission of the current transmit data has been completed.

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.

TDRE

TEND

1 frame

0/1

Data

Start

bit

Parity

bit

Stop

bit

Start

bit

Data

Parity

bit

Stop

bit

TXI interrupt

request generated

Data written to TDR and

TDRE flag cleared to 0 in

TXI interrupt service routine

TEI interrupt

request generated

Idle state

(mark state)

TXI interrupt

request generated

Figure 12.9 Example of Operation in Transmission in Asynchronous Mode

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

Figure 12.10 shows a sample flowchart for transmission in asynchronous mode.

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