TL16C752B-EP

3.3-V DUAL UART WITH 64-BYTE FIFO

SGLS153 – FEBRUARY 2003

6

POST OFFICE BOX 655303

functional description (continued)

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, the CTS state changes and need 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 can result. Figure 2 shows CTS functional timing, and Figure 3

shows an example of autoflow control.

Byte 0–7

Stop

Start

Byte 0–7

Stop

Start

TX

CTS

NOTES: A. When CTS is low, the transmitter keeps sending serial data out

B. When CTS goes high before the middle of the last stop bit of the current byte, the transmitter finishes sending the current byte but

it does not send the next byte.

C. When CTS goes from high to low, the transmitter begins sending data again.

Figure 2. CTS Functional Timing

Serial to

Parallel

Flow

Control

Parallel to

Serial

Flow

Control

RX

FIFO

TX

FIFO

Parallel to

Serial

Flow

Control

Serial to

Parallel

Flow

Control

TX

FIFO

RX

FIFO

D7–D0

D7–D0

UART 1

UART 2

RX

RTS

TX

CTS

TX

CTS

RX

RTS

Figure 3. Autoflow Control (Auto-RTS and Auto-CTS) Example