TL16C752B
3.3-V DUAL UART WITH 64-BYTE FIFO
SLLS405A – DECEMBER 1999 – REVISED AUGUST 2000
functional description (continued)
software flow control
Softwareflowcontrolisenabledthroughtheenhancedfeatureregisterandthemodemcontrolregister. Different
combinations of software flow control can be enabled by setting different combinations of EFR[3–0]. Table 1
shows software flow control options.
There are two other enhanced features relating to S/W flow control:
–
Xon Any Function [MCR(5)]: Operation will resume after receiving any character after recognizing the
Xoff character.
NOTE:
It is possible that an Xon1 character is recognized as an Xon Any character which could cause an
Xon2 character to be written to the RX FIFO.
–
Special Character [EFR(5)]: Incoming data is compared to Xoff2. Detection of the special character
setstheXoffinterrupt[IIR(4)]butdoesnothalttransmission. TheXoffinterruptisclearedbyareadofthe
IIR. The special character is transferred to the RX FIFO.
Table 1. Software Flow Control Options EFR[0:3]
BIT 3
BIT 2
BIT 1
BIT 0
Tx, Rx SOFTWARE FLOW CONTROLS
No transmit flow control
0
1
0
1
X
X
X
1
0
0
1
1
X
X
X
0
X
X
X
X
0
1
0
1
X
X
X
X
0
0
1
1
Transmit Xon1, Xoff1
Transmit Xon2, Xoff2
Transmit Xon1, Xon2: Xoff1, Xoff2
No receive flow control
Receiver compares Xon1, Xoff1
Receiver compares Xon2, Xoff2
Transmit Xon1, Xoff1
Receiver compares Xon1 and Xon2, Xoff1 and Xoff2
0
1
0
1
1
0
1
1
1
1
1
1
Transmit Xon2, Xoff2
Receiver compares Xon1 and Xon2, Xoff1 and 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
RX
When software flow control operation is enabled, the TL16C752B will compare incoming data with Xoff1/2
1
programmed characters (in certain cases Xoff1 and Xoff2 must be received sequentially ). When the correct
Xoff characters are received, transmission is halted after completing transmission of the current character. Xoff
detection also sets IIR[4] (if enabled via IER[5]) and causes INT to go high.
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 will be treated as normal data and will be written to the RCV FIFO.
1. When pairs of Xon/Xoff characters are programmed to occur sequentially, received Xon1/Xoff1 characters must be written to the Rx FIFO
if the subsequent character is not Xon2/Xoff2.
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