SC16IS741AIPW datasheet(8/55 Pages) NXP

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SC16IS741A

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Product data sheet

Rev. 1 — 18 March 2013

8 of 55

NXP Semiconductors

SC16IS741A

Single UART with I2C-bus/SPI interface, 64-byte FIFOs, IrDA SIR

7.3 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 4 shows software flow control options.

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

• Xon Any function (MCR[5]): Receiving any character will resume operation 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.

7.3.1 RX

When software flow control operation is enabled, the SC16IS741A will compare incoming

data with Xoff1/Xoff2 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 IRQ to go LOW.

To resume transmission, an Xon1/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.

Table 4.

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

EFR[3]

EFR[2]

EFR[1]

EFR[0]

TX, RX software flow control

no transmit flow control

transmit Xon1, Xoff1

transmit Xon2, Xoff2

transmit Xon1 and Xon2, Xoff1 and Xoff2

no receive flow control

receiver compares Xon1, Xoff1

receiver compares Xon2, Xoff2

1011transmit Xon1, Xoff1

receiver compares Xon1 or Xon2, Xoff1 or Xoff2

0111transmit Xon2, Xoff2

receiver compares Xon1 or Xon2, Xoff1 or Xoff2

1111transmit Xon1 and Xon2, Xoff1 and Xoff2

receiver compares Xon1 and Xon2, Xoff1 and Xoff2

0011no transmit flow control

receiver compares Xon1 and Xon2, Xoff1 and Xoff2

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