Section 16 Serial Communication Interface 3 (SCI3)
16.4.3
Data Transmission
Figure 16.5 shows an example of operation for transmission in asynchronous mode. In
transmission, the SCI3 operates as described below.
1. The SCI3 monitors the TDRE flag in SSR. If the flag is cleared to 0, the SCI3 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 SCI3 sets the TDRE flag to 1 and starts
transmission. If the TIE bit is set to 1 at this time, a TXI interrupt request 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. The SCI3 checks the TDRE flag at the timing for sending the stop bit.
4. 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.
5. 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 SCR3 is set to 1 at this time, a TEI
interrupt request is generated.
6. Figure 16.6 shows a sample flowchart for transmission in asynchronous mode.
Start
bit
Transmit
data
Parity Stop Start
Transmit
data
Parity Stop
Mark
state
bit
bit bit
bit
bit
Serial
data
1
0
D0 D1
D7 0/1
1
0
D0 D1
1 frame
D7 0/1
1
1
1 frame
TDRE
TEND
LSI
TXI interrupt
TDRE flag
cleared to 0
TXI interrupt request generated
TEI interrupt request
generated
operation request
generated
User
processing
Data written
to TDR
Figure 16.5 Example of SCI3 Transmission in Asynchronous Mode
(8-Bit Data, Parity, One Stop Bit)
Rev. 3.00 Sep. 10, 2007 Page 305 of 528
REJ09B0216-0300
RENESAS [ RENESAS TECHNOLOGY CORP ]
