NEC 78K0S/KB1+ User Manual page 202

(d) Continuous transmission
The next transmit data can be written to transmit buffer register 6 (TXB6) as soon as transmit shift register 6
(TXS6) has started its shift operation. Consequently, even while the INTST6 interrupt is being serviced after
transmission of one data frame, data can be continuously transmitted and an efficient communication rate
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can be realized. In addition, the next transmit data can be written to the TXB6 register without having to wait
for the transmission time of one data frame, by confirming bit 0 (TXSF6) of asynchronous serial interface
transmission status register 6 (ASIF6) after a transmission completion interrupt has occurred.
To transmit data continuously, be sure to reference the ASIF6 register to check the transmission status and
whether the TXB6 register can be written, and then write the data.
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For the continuous transmission procedure, refer to Figure 11-16 Example of Continuous Transmission
Processing Flow.
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Cautions 1. Use the value of the TXBF6 flag to judge whether continuous transmission is possible.
2. When the interface is used in LIN communication operation, the continuous
TXBF6
Caution To transmit data continuously, write the first transmit data (first byte) to the TXB6 register.
Be sure to check that the TXBF6 flag is "0". If so, write the next transmit data (second byte)
to the TXB6 register. If data is written to the TXB6 register while the TXBF6 flag is "1", the
transmit data cannot be guaranteed.
The communication status can be checked using the TXSF6 flag.
TXSF6
Caution To initialize the transmission unit upon completion of continuous transmission, be sure to
check that the TXSF6 flag is "0" after generation of the transmission completion interrupt,
and then execute initialization. If initialization is executed while the TXSF6 flag is "1", the
transmit data cannot be guaranteed.
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CHAPTER 11 SERIAL INTERFACE UART6
Do not write the next transmit data, by making a judgment only by the fact that the
TXSF6 flag has been set to 1.
transmission function cannot be used. Make sure that asynchronous serial interface
transmission status register 6 (ASIF6) is 00H before writing transmit data to transmit
buffer register 6 (TXB6).
0 Writing enabled
1 Writing disabled
0 Transmission is completed.
1 Transmission is in progress.
User's Manual U17446EJ3V1UD
Writing to TXB6 Register
Transmission Status