280
SCI3 operates as follows when transmitting data.
SCI3 monitors bit TDRE in SSR, and when it is cleared to 0, recognizes that data has been written
to TDR and transfers data from TDR to TSR. It then sets bit TDRE to 1 and starts transmitting. If
bit TIE in SCR3 is set to 1 at this time, a TXI request is made.
Serial data is transmitted from the TXD3x pin using the relevant data transfer format in table
10.11. When the stop bit is sent, SCI3 checks bit TDRE. If bit TDRE is cleared to 0, SCI3
transfers data from TDR to TSR, and when the stop bit has been sent, starts transmission of the
next frame. If bit TDRE is set to 1, bit TEND in SSR bit is set to 1the mark state, in which 1s are
transmitted, is established after the stop bit has been sent. If bit TEIE in SCR3 is set to 1 at this
time, a TEI request is made.
Figure 10.12 shows an example of the operation when transmitting in asynchronous mode.
1 frame
Start
bit
Start
bit
Transmit
data
Transmit
data
Parity
bit
Stop
bit
Parity
bit
Stop
bit
Mark
state
1 frame
0
1
D0
D1
D7
0/1
1
1
1
0
D0
D1
D7
0/1
Serial
data
TDRE
TEND
LSI
operation
TXI request
TDRE
cleared to 0
User
processing
Data written
to TDR
TXI request
TEI request
Figure 10.7 Example of Operation when Transmitting in Asynchronous Mode
(8-bit data, parity, 1 stop bit)