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Chapter 13
Serial Interface Function
Preliminary User’s Manual U15839EE1V0UM00
(3)
Asynchronous serial interface transmission status registers (ASIF0, ASIF1)
The ASIFn register, which consists of 2-bit status flags, indicates the status during transmission.
By writing the next data to the TXBn register after data is transferred from the TXBn register to the
transmission 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 ASIFn register to prevent writing to the TXBn register by mistake.
This register is read-only in 8-bit or 1-bit units (n = 0, 1).
Figure 13-4:
Asynchronous Serial Interface Transmit Status Registers (ASIF0, ASIF1)
The following table shows relationships between the transmission status and write operations to TXBn
register.
Caution:
When transmission is performed continuously, data should be written to TXBn
register after confirming the TXBF bit value. If writing is not permitted, transmit data
cannot be guaranteed when data is written to TXBn register.
7
6
5
4
3
2
1
0
Address
Initial
value
ASIF0
0
0
0
0
0
0
TXBF0
TXSF0
FFFF FA05H
00H
ASIF1
0
0
0
0
0
0
TXBF0
TXSF0
FFFF FA45H
00H
Bit Position
Bit Name
Function
1
TXBF
This is a transmission buffer data flag.
0: When the ASIMn register’s Power or TXE bits is 0, or when data has
been transferred to the transmission shift register (Data to be transferred
next to TXBn register does not exist).
1: Data exists in TXBn register when the TXBn register has been written to
(Data to be transferred next exists in TXBn register).
0
TXSF
This is a transmission shift register data flag. It indicates the transmission
status of UART5n.
0: When the ASIMn register’s Power or TXE bits is set to 0, or when follow-
ing transfer completion, the next data transfer from the TXBn register is
not performed (waiting transmission)
1: When data has been transferred from the TXBn register (Transmission in
progress)
TXBF
TXSF
Transmission Status
Write Operation to
TXBn
0
0
Initial status or transmission completed
Writing is permitted
0
1
Transmission in progress (no data is in TXBn)
Writing is permitted
1
0
Waiting transmission (data is in TXBn)
Writing is not permitted
1
1
Transmission in progress (data is in TXBn)
Writing is not permitted
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