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SCI3 operates as follows during data transmission in asynchronous mode.
SCI3 monitors bit TDRE in SSR. When this bit is cleared to 0, SCI3 recognizes that there is data
written in the transmit data register (TDR), which it transfers to the transmit shift register (TSR).
Then TDRE is set to 1 and transmission starts. If bit TIE in SCR3 is set to 1, a TXI interrupt is
requested.
Serial data is transmitted from pin TXD using the communication format outlined in
table 10.14. After that, it checks TDRE at the same timing which it transmits the stop bit.
If TDRE is 0, data is transferred from TDR to TSR, and after the stop bit is sent, transmission of
the next frame starts. If TDRE is 1, the TEND bit in SSR is set to 1, and after the stop bit is sent,
the “mark state” is entered, in which 1 is continuously output. A TEI interrupt is requested in this
state if bit TEIE in SCR3 is set to 1.
Figure 10.9 shows a typical operation in asynchronous transmission mode.
0
D0
D1
D7
0/1
1
D0
D1
D7
0/1
1
0
Start
bit
Parity
bit
Stop
bit
Parity
bit
Stop
bit
1
Start
bit
Mark
state
TDRE
TEND
TXI request
TEI request
1 frame
TXI request
Serial
data
Transmit
data
Transmit
data
1 frame
SCI3
operation
User
processing
TDRE cleared to 0
1
Write data in TDR
Figure 10.9 Typical Transmit Operation in Asynchronous Mode
(8-Bit Data, Parity Bit Added, and 1 Stop Bit)
Receiving: Figure 10.10 shows a typical flow chart for receiving serial data. After SCI3
initialization, follow the procedure below.