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XC161 Derivatives
Peripheral Units (Vol. 2 of 2)
Asynchronous/Synchronous Serial Interface (ASC)
User’s Manual
18-10
V2.2, 2004-01
ASC_X, V2.0
Figure 18-7
Transmit FIFO Operation Example
The example in
shows a typical 8-stage transmit FIFO operation. In this
example seven bytes are transmitted via the TxD output line. The transmit FIFO interrupt
trigger level TXFITL is set to 0011
B
. The first byte written into the empty TXFIFO via
TBUF is directly transferred into the transmit shift register and is not written into the FIFO.
A transmit buffer interrupt will be generated in this case. After byte 1, bytes 2 to 6 are
written into the transmit FIFO.
After the transfer of byte 3 from the TXFIFO into the transmit shift register of the ASC,
3 bytes remain in the TXFIFO. Therefore, the value of TXFITL is reached and a transmit
buffer interrupt will be generated at the beginning and a transmit interrupt at the end of
the byte 3 serial transmission. During the serial transmission of byte 4, another byte
(byte 7) is written into the TXFIFO (TBUF write operation). Finally, after the start of the
serial transmission of byte 7, the TXFIFO is again empty.
MCT05438
Byte 6
Byte 5
Byte 4
Byte 3
0101
Byte 2
TBIR
0100
Byte 3
TIR
TBIR
0011
TIR
TBIR
0010
Byte 5
TIR
TBIR
0010
Byte 7
Byte 6
TIR
TIR
TBIR
0001
0000
0000
TxD
FSTAT.
TXFFL
Byte 6
Byte 5
Byte 4
Byte 6
Byte 5
Byte 6
Byte 5
Byte 7
Byte 6
Byte 7
Byte 7
TXFIFO
Empty
Byte 6
Byte 5
Byte 4
Byte 3
Byte 2
Byte 5
Byte 4
Byte 3
Byte 2
Byte 4
Byte 3
Byte 2
Byte 3
Byte 2
Byte 2
Writing Byte 1
Writing Byte 2
Writing Byte 3
Writing Byte 4
Writing Byte 5
Writing Byte 6
Writing Byte 7
TXFCON.TXFITL = 0011
B
Byte 1
Byte 4
TBIR