NEC mPD789101 User Manual page 185

(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 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 13-8. Asynchronous Serial Interface Transmission Completion Interrupt Timing
TxD20 (Output)
START
INTST20
TxD20 (Output)
START
INTST20
Caution Do not rewrite asynchronous serial interface mode register 20 (ASIM20) during a transmit
operation. If ASIM20 register is rewritten during transmission, subsequent transmission
may not 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.
CHAPTER 13 SERIAL INTERFACE 20
(a) Stop bit length: 1
D0 D1 D2
(b) Stop bit length: 2
D0 D1 D2
User's Manual U13045EJ2V0UM00
STOP
D6 D7 Parity
D6 D7 Parity
STOP
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