SC16C752IB48 datasheet(9/47 Pages) PHILIPS

9 / 47 page

Philips Semiconductors

SC16C752

Dual UART with 64-byte FIFO

Product data

Rev. 04 — 20 June 2003

9 of 47

9397 750 11635

6.3 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 3 shows software ﬂow

control options.

Remark: When using software ﬂow control, the Xon/Xoff characters cannot be used

for data characters.

There are two other enhanced features relating to software ﬂow control:

• Xon Any function (MCR[5]): Operation will resume after receiving any character

after recognizing the Xoff character. 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.

6.3.1

When software ﬂow control operation is enabled, the SC16C752 will compare

incoming data with Xoff1,2 programmed characters (in certain cases, Xoff1 and Xoff2

must be received sequentially). When the correct Xoff character 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.

Table 3:

Software ﬂow control options (EFR[0:3])

EFR[3]

EFR[2]

EFR[1]

EFR[0]

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 compared Xon1, Xoff1

receiver compares Xon2, Xoff2

1011transmit Xon1, Xoff1

receiver compares Xon1 and Xon2, Xoff1 and Xoff2

0111transmit Xon2, Xoff2

receiver compares Xon1 and Xon2, Xoff1 and Xoff2

1111transmit Xon1, Xon2, Xoff1, Xoff2

receiver compares Xon1 and Xon2, Xoff1 and Xoff2

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