SC16IS752IPW datasheet(10/59 Pages) NXP

10 / 59 page

SC16IS752_SC16IS762_7

Product data sheet

Rev. 07 — 19 May 2008

10 of 59

NXP Semiconductors

SC16IS752/SC16IS762

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

7.2.2 Auto-CTS

Figure 6 shows CTS functional timing. The transmitter circuitry checks CTS before

sending the next data character. When CTS is active, the transmitter sends the next

character. To stop the transmitter from sending the following character, CTS must be

deasserted before the middle of the last stop bit that is currently being sent. The

Auto-CTS function reduces interrupts to the host system. When ﬂow control is enabled,

CTS level changes do not trigger host interrupts because the device automatically

controls its own transmitter. Without Auto-CTS, the transmitter sends any data present in

the transmit FIFO and a receiver overrun error may result.

7.3 Software ﬂow control

Software ﬂow control is enabled through the Enhanced Features 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.

(1) When CTS is LOW, the transmitter keeps sending serial data out.

(2) When CTS goes HIGH before the middle of the last stop bit of the current character, the transmitter ﬁnishes sending the current

character, but it does not send the next character.

(3) When CTS goes from HIGH to LOW, the transmitter begins sending data again.

Fig 6.

CTS functional timing

start

bit 0 to bit 7

stop

CTS

002aab041

start

stop

bit 0 to bit 7

Table 3.

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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