NEC uPD78P078 User Manual
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CHAPTER 20 SERIAL INTERFACE CHANNEL 2
(c) Transmission
A transmit operation is started by writing transmit data to the transmit shift register (TXS). The start
bit, parity bit, and stop bit(s) are added automatically.
When the transmit operation starts, the data in the transmit shift register (TXS) is shifted out, and when
the transmit shift register (TXS) is empty, a transmission completion interrupt request (INTST) is
generated.
Figure 20-8. Asynchronous Serial Interface Transmission Completion Interrupt Request Generation Timing
(a) Stop bit length: 1
(b) Stop bit length: 2
Caution The asynchronous serial interface mode register (ASIM) should not be rewritten
during a transmit operation. If the ASIM register is rewritten during transmission,
subsequent transmit operations may not be possible (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 request (INTST) or the interrupt request flag
(STIF) set by the INTST.
D1
D2
D6
D7
Parity
D0
TxD (Output)
INTST
STOP
START
D1
D2
D6
D7
Parity
D0
TxD (Output)
INTST
STOP
START