Philips Semiconductors

SC16C752

Dual UART with 64-byte FIFO

Product data

Rev. 04 — 20 June 2003

8 of 47

9397 750 11635

© Koninklijke Philips Electronics N.V. 2003. All rights reserved.

6.2.1

Auto-RTS

Auto-RTS data flow control originates in the receiver block (see Figure 1 “Block

diagram.” on page 3). Figure 4 shows RTS functional timing. The receiver FIFO

trigger levels used in Auto-RTS are stored in the TCR. RTS is active if the RX FIFO

level is below the halt trigger level in TCR[3:0]. When the receiver FIFO halt trigger

level is reached, RTS is deasserted. The sending device (e.g., another UART) may

send an additional byte after the trigger level is reached (assuming the sending UART

has another byte to send) because it may not recognize the deassertion of RTS until

it has begun sending the additional byte. RTS is automatically reasserted once the

receiver FIFO reaches the resume trigger level programmed via TCR[7:4]. This

reassertion allows the sending device to resume transmission.

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.

(1) N = receiver FIFO trigger level.

(2) The two blocks in dashed lines cover the case where an additional byte is sent, as described in Section 6.2.1.

Fig 4.

RTS functional timing.

START

BYTE N

START

BYTE N + 1

START

STOP

STOP

RX

RTS

IOR

N

N+1

12

002aaa226

(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 5.

CTS functional timing.

START

BYTE 0-7

STOP

TX

CTS

002aaa227

START

BYTE 0-7

STOP