TL16CP754C Datasheet, PDF (10/49 Pages) Texas Instruments – QUAD UARTS WITH 64-BYTE FIFO

TL16CP754C, TL16CM754C, TL16C754C
SLLS644E – DECEMBER 2007 – REVISED MAY 2010
BIT 3
0
1
0
1
X
X
X
1
0
1
0
Table 1. Software Flow Control Options EFR[3:0]
BIT 2
0
0
1
1
X
X
X
0
1
1
0
BIT 1
X
X
X
X
0
1
0
1
1
1
1
BIT 0
X
X
X
X
0
0
1
1
1
1
1
Tx, Rx SOFTWARE FLOW CONTROLS
No transmit flow control
Transmit Xon1, Xoff1
Transmit Xon2, Xoff2
Transmit Xon1, Xon2: Xoff1, Xoff2
No receive flow control
Receiver compares Xon1, Xoff1 X X 0 1
Receiver compares Xon2, Xoff2
Transmit Xon1, Xoff1
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
Transmit Xon2, Xoff2
Receiver compares Xon1 or Xon2, Xoff1 or Xoff2
Transmit Xon1, Xon2: Xoff1, Xoff2
Receiver compares Xon1 and Xon2: Xoff1 and Xoff2
No transmit flow control
Receiver compares Xon1 and Xon2: Xoff1 and Xoff2
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When software flow control operation is enabled, the '754C compares incoming data with Xoff1/2 programmed
characters (in certain cases Xoff1 and Xoff2 must be received sequentially⁽¹⁾). When an Xoff character is
received, transmission is halted after completing transmission of the current character. Xoff character detection
also sets IIR[4] and causes INT to go high (if enabled via IER[5]).
To resume transmission an Xon1/2 character must be received (in certain cases Xon1 and Xon2 must be
received sequentially). When the correct Xon characters are received IIR[4] is cleared and the Xoff interrupt
disappears.
NOTE
If a parity, framing or break error occurs while receiving a software flow control character,
this character is treated as normal data and is written to the RCV FIFO.
Xoff1/2 characters are transmitted when the RX FIFO has passed the programmed trigger level TCR[3:0].
Xon1/2 characters are transmitted when the RX FIFO reaches the trigger level programmed via TCR[7:4].
NOTE
If, after an Xoff character has been sent, software flow control is disabled, the UART
transmits Xon characters automatically to enable normal transmission to proceed. A
feature of the '754C 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 is 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 are transmitted. 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 are never enabled simultaneously. Figure 4
shows a software flow control example.
(1) When pairs of Xon/Xoff characters are programmed to occur sequentially, received Xon1/Xoff1 characters will be written to the Rx FIFO
if the subsequent character is not Xon2/Xoff2.
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