Datasheet

UART 1
ParalleltoSerial
SerialtoParallel
Xon-1 Word
Xon-2Word
Xoff-1 Word
Xoff-1Word
SerialtoParallel
ParalleltoSerial
Xon-1 Word
Xoff-1 Word
Xoff-2Word
Data
XoffXonXoff
UART 2
Xon-2 Word
Transmit
FIFO
Receive
FIFO
Compare
Programmed
XonXoff
Characters
B0417-01
TL16C752B
SLLS405C –DECEMBER 1999–REVISED JUNE 2010 www.ti.com
TX
Xoff1/2 characters are transmitted when the RX FIFO has passed the HALT trigger level programmed in
TCR[3:0].
Xon1/2 characters are transmitted when the RX FIFO reaches the RESUME trigger level programmed in
TCR[7:4].
An important note here is that if, after an xoff character has been sent and software flow control is disabled, the
UART will transmit Xon characters automatically to enable normal transmission to proceed. A feature of the
TL16C752B UART design is that if the software flow combination (EFR[3:0]) changes after an Xoff has been
sent, the originally programmed Xon is automatically sent. If the RX FIFO is still above the trigger level, the newly
programmed Xoff1/2 will be transmitted.
The transmission of Xoff/Xon(s) follows the exact same protocol as transmission of an ordinary byte from the
FIFO. This means that even if the word length is set to be 5, 6, or 7 characters then the 5, 6, or 7 least significant
bits of Xoff1, 2/Xon1, 2 will be transmitted. (Note that the transmission of 5, 6, or 7 bits of a character is seldom
done, but this functionality is included to maintain compatibility with earlier designs.)
It is assumed that software flow control and hardware flow control will never be enabled simultaneously. Figure 4
shows an example of software flow control.
Figure 4. Software Flow Control Example
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