Transmitting Serial Data (Asynchronous Mode): Figure 13-5 shows a sample flowchart for
transmitting serial data and indicates the procedure to follow.
Figure 13-5 Sample Flowchart for Transmitting Serial Data
Start transmitting
Read TDRE flag in SSR
TDRE = 1?
Write transmit data
in TDR and clear TDRE
flag to 0 in SSR
All data
transmitted?
End
1
2
3
No
Yes
No
Yes
SCI initialization: the transmit data output function
of the TxD pin is selected automatically.
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.
Read TEND flag in SSR
TEND = 1?
No
Yes
Output break
signal?
No
Yes
Clear TE bit to 0 in SCR
4
1.
2.
3.
4.
Clear DR bit to 0,
set DDR bit to 1
Initialize
To continue transmitting serial data: after checking
that the TDRE flag is 1, indicating that data can be
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,
the TDRE flag is checked and cleared automatically.
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.
470
www.DataSheet4U.com
