CHAPTER 12 SERIAL INTERFACE 20
(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
TxD20 (output)
INTST20
D0
D1
D2
D6
D7
Parity
START
(b) Stop bit length: 2
D0
D1
D2
D6
D7
Parity
TxD20 (output)
INTST20
STOP
START
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.
User’s Manual U15075EJ1V0UM00
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NEC [ NEC ]
