NEC PD78F9488 - Manual (Page 206)

CHAPTER 11 SERIAL INTERFACE 20
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User’s Manual U15331EJ4V1UD
(c) Transmission
A transmit operation is started by writing transmit data to transmit 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 11-8. 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.