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CHAPTER 14 SERIAL INTERFACE UART
(c) Transmission
The transmit operation is started when transmit data is written to the transmit shift register (TXS). A start
bit, parity bit, and stop bit(s) are automatically added to the data.
Starting the transmit operation shifts out the data in TXS, thereby emptying TXS, after which a transmit
completion interrupt (INTST) is issued.
The timing of the transmit completion interrupt is shown in Figure 14-7.
Figure 14-7. Timing of Asynchronous Serial Interface Transmit Completion Interrupt
TxD (output)
D0
D1
D2
D6
D7
Parity
STOP
START
INTST
(i) Stop bit length: 1 bit
TxD (output)
D0
D1
D2
D6
D7
Parity
START
INTST
(ii) Stop bit length: 2 bits
STOP
Caution
Do not rewrite the asynchronous serial interface mode register (ASIM) during a transmit
operation. Rewriting to the ASIM register during a transmit operation may disable
further transmit operations (in such case, enter a RESET to restore normal operation).
Whether or not a transmit operation is in progress can be determined by software using
the transmit completion interrupt (INTST) or the interrupt request flag (STIF) that is set
by INTST.
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