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Auto-CTS (See Figure 2)

Enabling Autoflow Control and Auto-CTS

Auto-CTS and Auto-RTS Functional Timing

Start

Bits 0 −7

Start

Bits 0 −7

Start

Bits 0 −7

Stop

Stop

Stop

SOUT

CTS

Start

Byte N

Start

Byte N+1

Start

Byte

Stop

Stop

Stop

SIN

RTS

RD

(RD RBR)

1

2

N

N+1

Byte 14

Byte 15

SIN

RTS

RD

(RD RBR)

Start

Byte 18

Stop

Start

Byte 16

Stop

RTS Released After the

First Data Bit of Byte 16

TL16C2552

SLWS163A – SEPTEMBER 2005 – REVISED JUNE 2006

The transmitter circuitry checks CTS before sending the next data byte. When CTS is active, it sends the next

byte. To stop the transmitter from sending the following byte, CTS must be released before the middle of the last

stop bit that is currently being sent (see Figure 2). 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.

Autoflow control is enabled by setting modem control register bits 5 (autoflow enable or AFE) and 1 (RTS) to a

1. Autoflow incorporates both auto-RTS and auto-CTS. When only auto-CTS is desired, bit 1 in the modem

control register should be cleared (this assumes that a control signal is driving CTS).

Figure 2. CTS Functional Timing Waveforms

Figure 3. RTS Functional Timing Waveforms, RCV FIFO Trigger Level = 1, 4, or 8 Bytes

Figure 4. RTS Functional Timing Waveforms, RCV FIFO Trigger Level = 14 Bytes

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