Philips Semiconductors

SC16C752B

5 V, 3.3 V and 2.5 V dual UART, 5 Mbit/s (max.), with 64-byte FIFOs

Product data

Rev. 03 — 14 December 2004

9 of 47

9397 750 14443

© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

6.2.2

Auto-CTS

The transmitter circuitry checks CTS before sending the next data byte. When CTS is

active, the transmitter sends the next byte. To stop the transmitter from sending the

following byte, 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.

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.

(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 byte, the transmitter finishes sending the current

byte, but is does not send the next byte.

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

Fig 6.

CTS functional timing.

Start

byte 0 to 7

Stop

TX

CTS

002aaa227

Start

byte 0 to 7

Stop

Table 3:

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

EFR[3]

EFR[2]

EFR[1]

EFR[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 compared Xon1, Xoff1

X

X

0

1

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