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-
14. 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.
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 request
TDRE
TXI request
TEI request
operation
cleared to 0
User
processing
Data written
to TDR
Figure 10-12 Example of Operation when Transmitting in Asynchronous Mode
(8-bit data, parity, 1 stop bit)
300
ETC [ ETC ]
