TL16C752B-EP

3.3-V DUAL UART WITH 64-BYTE FIFO

SGLS153 – FEBRUARY 2003

7

POST OFFICE BOX 655303

functional description (continued)

software flow control

Software flow control is enabled through the enhanced feature register and the modem control register. 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 resumes 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

sets the Xoff interrupt [IIR(4)] but does not halt transmission. The Xoff interrupt is cleared by a read of the

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

0

0

X

X

No transmit flow control

1

0

X

X

Transmit Xon1, Xoff1

0

1

X

X

Transmit Xon2, Xoff2

1

1

X

X

Transmit Xon1, Xon2: Xoff1, Xoff2

X

X

0

0

No receive flow control

X

X

1

0

Receiver compares Xon1, Xoff1

X

X

0

1

Receiver compares Xon2, Xoff2

1

0

1

1

Transmit Xon1, Xoff1

Receiver compares Xon1 and Xon2, Xoff1 and Xoff2

0

1

1

1

Transmit Xon2, Xoff2

Receiver compares Xon1 and Xon2, Xoff1 and Xoff2

1

1

1

1

Transmit Xon1, Xon2: Xoff1, Xoff2

Receiver compares Xon1 and Xon2: Xoff1 and Xoff2

0

0

1

1

No transmit flow control

Receiver compares Xon1 and Xon2: Xoff1 and Xoff2

RX

When software flow control operation is enabled, the TL16C752B-EP compares incoming data with Xoff1/2

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 is treated as normal data and is 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.