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www.diodes.com

April 2019

Diodes Incorporated

PI7C9X760

Document Number DS40305 Rev 6-2

A product Line of

Diodes Incorporated

PI7C9X760

2.1 Auto-RTS

Figure 2 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 character after the trigger level is reached (assuming the

sending UART has another character to send) because it may not recognize the de-assertion of RTS until it has begun sending the ad-

ditional character. 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.

2.2 Auto-CTS

Figure 3 shows CTS functional timing. The transmitter circuitry checks CTS before sending the next data character. When CTS is ac-

tive, the transmitter sends the next character. To stop the transmitter from sending the following character, CTS must be de-asserted

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.

RX

IRQ#

Start

Figure 2. RTS functional timing

Receive

FIFO

Read

character

N

Stop

Start

character

N + 1

Stop

Start

1

2

N

N + 1

002aab040

(1) N = receiver FIFO trigger level.

(2) The two blocks in dashed lines cover the case where an additional character is sent.

TX

Start

Figure 3. CTS functional timing

character

N

Stop

Stop

002aab041

(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.

Start

bit 0 to bit 7

CTS