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Section 13 Serial Communication Interface (SCI)
13.4.5
Serial Data Transmission (Asynchronous Mode)
Figure 13.6 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 it 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 in SCR is set to 1 at this time, a TXI interrupt request is generated.
Because the TXI interrupt processing 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 next transmit 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 13.7 shows a sample flowchart for transmission in asynchronous mode.
Start
bit
1
TDRE
TEND
TXI interrupt
request generated
Figure 13.6 Example of Operation for Transmission in Asynchronous Mode
Rev.2.00 Jun. 28, 2007 Page 486 of 666
REJ09B0311-0200
Data
Parity
bit
0
D0
D1
D7
Data written to TDR and
TDRE flag cleared to 0 in
TXI interrupt processing
routine
1 frame
(Example with 8-Bit Data, Parity, One Stop Bit)
Stop
Start
bit
bit
0/1
1
0
D0
D1
TXI interrupt
request generated
Data
Parity
Stop
bit
bit
1
Idle state
D7
0/1
1
(mark state)
TEI interrupt
request generated
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