CHAPTER 10 SERIAL INTERFACE FUNCTION
User’s Manual U14492EJ3V0UD
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(3) Continuous transmission operation
UART0 can write the next transmit data to the TXB0 register at the timing that the transmission shift register
starts the shift operation. This enables an efficient transmission rate to be realized by continuously
transmitting data even during the INTST0 interrupt service after the transmission of one data frame. In
addition, reading the TXSF0 bit of the ASIF0 register after the occurrence of a transmission completion
interrupt enables the TXB0 register to be efficiently written twice (2 bytes) without waiting for the transmission
of 1 data frame.
When continuous transmission is performed, data should be written after referencing the ASIF0 register to
confirm the transmission status and whether or not data can be written to the TXB0 register.
TXBF0
Whether or Not Writing to TXB0 Register Is Enabled
0
Writing is enabled
1
Writing is not enabled
Caution
When transmission is performed continuously, write the first transmit data (first byte) to the
TXB0 register and confirm that the TXBF0 bit is 0, and then write the next transmit data
(second byte) to TXB0 register. If writing to the TXB0 register is performed when the TXBF0
bit is 1, transmit data cannot be guaranteed.
While transmission is being performed continuously, whether writing to the TXB0 register later is enabled can
be judged by confirming the TXSF0 bit after the occurrence of a transmission completion interrupt.
TXSF0
Transmission Status
0
Transmission is completed. However, the cautions concerning the TXBF0 bit
must be observed. Writing transmit data can be performed twice (2 bytes).
1
Under transmission. Transmit data can be written once (1 byte).
Cautions 1.
When initializing the transmission unit when continuous transmission is completed,
confirm that the TXSF0 bit is 0 after the occurrence of the transmission completion
interrupt, and then execute initialization. If initialization is performed when the TXSF0
bit is 1, transmit data cannot be guaranteed.
2. While transmission is being performed continuously, an overrun error may occur if the
next transmission is completed before the INTST0 interrupt servicing following the
transmission of 1 data frame is executed. An overrun error can be detected by
embedding a program that can count the number of transmit data and referencing
TXSF0 bit.
