SC16C754BIA68,529

SC16C754B_4 © NXP B.V. 2008. All rights reserved.

6.2.1 Auto-RTS

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

SC16C754B”). Figure 6 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

de-asserted. The sending device (for example, 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 de-assertion 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 re-assertion allows the sending

device to resume transmission.

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.

N = receiver FIFO trigger level.

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