CHAPTER 12 SERIAL INTERFACE 20
User’s Manual U15075EJ1V0UM00
233
(c) Transmission
A transmit operation is started by writing transmit data to transmission shift register 20 (TXS20). The
start bit, parity bit, and stop bit(s) are added automatically.
When the transmit operation starts, the data in TXS20 is shifted out, and when TXS20 is empty, a
transmission completion interrupt (INTST20) is generated.
Figure 12-8. Asynchronous Serial Interface Transmission Completion Interrupt Timing
(a) Stop bit length: 1
STOP
Parity
D7
D6
D2
D1
D0
START
TxD20 (output)
INTST20
(b) Stop bit length: 2
STOP
Parity
D7
D6
D2
D1
D0
START
TxD20 (output)
INTST20
Caution
Do not rewrite asynchronous serial interface mode register 20 (ASIM20) during a
transmit operation. If the ASIM20 register is rewritten during transmission,
subsequent transmission may not be able to be performed (the normal state is
restored by RESET input).
It is possible to determine whether transmission is in progress by software by using a
transmission completion interrupt (INTST20) or the interrupt request flag (STIF20) set
by INTST20.
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