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Transmitting Serial Data (Asynchronous Mode): Figure 13-5 shows a sample flowchart for
transmitting serial data and indicates the procedure to follow.
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Initialize
Start transmitting
Read TDRE flag in SSR
TDRE = 1?
Yes
Write transmit data
in TDR and clear TDRE
flag to 0 in SSR
All data
transmitted?
Yes
Read TEND flag in SSR
TEND = 1?
Yes
Output break
signal?
Yes
Clear DR bit to 0,
set DDR bit to 1
Clear TE bit to 0 in SCR
End
Figure 13-5 Sample Flowchart for Transmitting Serial Data
1
1.
SCI initialization: the transmit data output function
of the TxD pin is selected automatically.
2.
SCI status check and transmit data write: read SSR,
check that the TDRE flag is 1, then write transmit data
in TDR and clear the TDRE flag to 0.
3.
To continue transmitting serial data: after checking
that the TDRE flag is 1, indicating that data can be
2
written, write data in TDR, then clear the TDRE
flag to 0. When the DMAC is activated by a transmit-
-data-empty interrupt request (TXI) to write data in TDR,
No
the TDRE flag is checked and cleared automatically.
4.
To output a break signal at the end of serial transmission:
set the DDR bit to 1 and clear the DR bit to 0
(DDR and DR are I/O port registers), then clear the
TE bit to 0 in SCR.
No
3
No
No
4
470
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