
CHAPTER 15 ASYNCHRONOUS SERIAL INTERFACE (UART)
User
’
s Manual U15862EJ3V0UD
456
15.6.3 Continuous transmission operation
UARTn can write the next transmit data to the TXBn 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 INTSTn interrupt service after the transmission of one data frame. In addition, reading the TXSFn bit of the
ASIFn register after the occurrence of a transmission completion interrupt enables the TXBn 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 ASIFn register to confirm
the transmission status and whether or not data can be written to the TXBn register.
TXBFn
Whether or Not Writing to TXBn 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
TXBn register and confirm that the TXBFn bit is 0, and then write the next transmit data (second
byte) to TXBn register. If writing to the TXBn register is performed when the TXBFn bit is 1,
transmit data cannot be guaranteed.
While transmission is being performed continuously, whether writing to the TXBn register later is enabled can be
judged by confirming the TXSFn bit after the occurrence of a transmission completion interrupt.
TXSFn
Transmission Status
0
Transmission is completed. However, the cautions concerning the TXBFn 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 TXSFn bit is 0 after the occurrence of the transmission completion interrupt, and
then execute initialization. If initialization is performed when the TXSFn 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 INTSTn 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 TXSFn bit.