NEC mPD780065 Series Preliminary User's Manual page 203

(c) Transmission
The transmit operation is started when transmit data is written to the transmit shift register (TXS0). A start
bit, parity bit, and stop bit(s) are automatically added to the data.
Starting the transmit operation shifts out the data in TXS0, thereby emptying TXS0, after which a transmit
completion interrupt request (INTST0) is issued.
The timing of the transmit completion interrupt request is shown in Figure 13-7.
Figure 13-7. Timing of Asynchronous Serial Interface Transmit Completion Interrupt Request
(i) Stop bit length: 1 bit
TxD0 (output) START
INTST0
(ii) Stop bit length: 2 bits
TxD0 (output) START
INTST0
Caution Do not rewrite to the asynchronous serial interface mode register (ASIM0) during a
transmit operation. Rewriting ASIM0 register during a transmit operation may disable
further transmit operations (in such cases, enter a RESET to restore normal operation).
Whether or not a transmit operation is in progress can be determined via software using
the transmit completion interrupt request (INTST0) or the interrupt request flag (STIF0)
that is set by INTST0.
CHAPTER 13 SERIAL INTERFACE (UART0)
D0 D1 D2
D0 D1 D2
Preliminary User's Manual U13420EJ2V0UM00
D6 D7 Parity
STOP
D6 D7 Parity STOP
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