9.3.4 Auto-RTS

Auto-RTS data flow control originates in the receiver block (see Figure 18). Figure 20 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 (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 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.

A. N = receiver FIFO trigger level B.

B. The two blocks in dashed lines cover the case where an additional byte is sent as described in Auto-RTS.

Figure 20. RTS Functional Timing