TL16C752CI-Q1_16 Datasheet, PDF (20/57 Pages) Texas Instruments – Dual UART

TL16C752CI-Q1
SLLSEQ9A – OCTOBER 2015 – REVISED FEBRUARY 2016
www.ti.com
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
When software flow control operation is enabled, the TL16C752CI-Q1 device compares incoming data with Xoff1
and Xoff2 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 and Xon2 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 and Xoff2 characters are transmitted when the RX FIFO has passed the programmed trigger level
TCR[3:0].
Xon1 and Xon2 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 TL16C752CI-Q1 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 or Xoff2 is transmitted.
The transmission of Xoff and Xon 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, Xoff2 and Xon1, Xon2 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 19
shows a software flow control example.
(1) When pairs of Xon and Xoff characters are programmed to occur sequentially, received Xon1 and Xoff1 characters will be written to the
RX FIFO if the subsequent character is not Xon2 and Xoff2.
20
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