NEC PD703114 User Manual page 415

(3) Asynchronous serial interface transmission status register 0 (ASIF0)
The ASIF0 register, which consists of 2-bit status flags, indicates the status during transmission.
By writing the next data to the TXB0 register after data is transferred from the TXB0 register to the transmit
shift register, transmit operations can be performed continuously without suspension even during an interrupt
interval. When transmission is performed continuously, data should be written after referencing the TXBF0
bit of the ASIF0 register to prevent writing to the TXB0 register by mistake.
This register is read-only, in 8-bit or 1-bit units.
7 6
ASIF0 0 0
Bit position Bit name
1 TXBF0
0 TXSF0
CHAPTER 10 SERIAL INTERFACE FUNCTION
5 4 3
0 0 0
This is a transmit buffer data flag.
0: Data to be transferred next to TXB0 register does not exist (When the ASIM0
register's UARTCAE0 or TXE0 bits is 0, or when data has been transferred to
the transmit shift register)
1: Data to be transferred next exists in TXB0 register (Data exists in TXB0
register when the TXB0 register has been written to)
Caution When transmission is performed continuously, data should be
written to the TXB0 register after confirming that this flag is 0. If
writing to TXB0 register is performed when this flag is 1, transmit
data cannot be guaranteed.
This is a transmit shift register data flag. It indicates the transmission status of
UART0.
0: Initial status or a waiting transmission (When the ASIM0 register's UARTCAE0
or TXE0 bits is set to 0, or when following transmission completion, the next
data transfer from the TXB0 register is not performed)
1: Transmission in progress (When data has been transferred from the TXB0
register)
Caution When the transmission unit is initialized, initialization should be
executed after confirming that this flag is 0 following the
occurrence of a transmission completion interrupt (INTST0). If
initialization is performed when this flag is 1, transmit data cannot
be guaranteed.
User's Manual U15195EJ5V0UD
2 <1> <0>
0 TXBF0 TXSF0 FFFFFA05H
Function
Address After reset
00H
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