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10. Serial Communication Interface
SCI3 operates as follows during data transmission using a multiprocessor format.
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.
Next, TDRE is checked as the stop bit is being transmitted. 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 output remains at 1 (mark state). A
TEI interrupt is requested in this state if bit TEIE in SCR3 is set to 1.
Figure 10.22 shows a typical SCI3 operation in multiprocessor communication mode.
Start
bit
Serial
1
0
D0
data
TDRE
TEND
LSI
TXI request
operation
User
processing
Figure 10.22 Typical Multiprocessor Format Transmit Operation
(8-Bit Data, Multiprocessor Bit Added, and 1 Stop Bit)
Rev.3.00 Jul. 19, 2007 page 302 of 532
REJ09B0397-0300
Transmit
MPB
data
D1
D7
0/1
1 frame
TDRE cleared
TXI
to 0
request
Write data in
TDR
Stop
Start
Transmit
bit
bit
data
1
0
D0
D1
Stop
MPB
bit
D7
0/1
1
1 frame
TEI
request
Mark
state
1
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