TL16C554APNR datasheet(33/46 Pages) TI1

33 / 46 page

TL16C554A, TL16C554AI

ASYNCHRONOUS-COMMUNICATIONS ELEMENT

SLLS509E − AUGUST 2001 − REVISED JUNE 2010

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

autoflow control (see Figure 20)

Autoflow control is comprised of auto-CTS and auto-RTS. With auto-CTS, the CTS input must be active before

the transmitter FIFO can send data. With auto-RTS, RTS becomes active when the receiver can handle more

data and notifies the sending serial device. When RTS is connected to CTS, data transmission does not occur

unless the receiver FIFO has space for the data; thus, overrun errors are eliminated using ACE1 and ACE2 from

a TL16C554A with the autoflow control enabled. Otherwise, overrun errors may occur when the transmit-data

rate exceeds the receiver FIFO read latency.

RCV

FIFO

Serial to

Parallel

Flow

Control

XMT

FIFO

Parallel

to Serial

Flow

Control

Parallel

to Serial

Flow

Control

Serial to

Parallel

Flow

Control

XMT

FIFO

RCV

FIFO

ACE1

ACE2

D7 − D0

SIN

SOUT

RTS

CTS

SOUT

SIN

CTS

RTS

D7 − D0

Figure 20. Autoflow Control (Auto-RTS and Auto-CTS) Example

auto-RTS (see Figure 20)

Auto-RTS data flow control originates in the receiver timing and control block (see functional block diagram)

and is linked to the programmed receiver FIFO trigger level. When the receiver FIFO level reaches a trigger level

of 1, 4, or 8 (see Figure 22) RTS is deasserted. With trigger levels of 1, 4, and 8, the sending ACE may send

an additional byte after the trigger level is reached (assuming the sending ACE has another byte to send)

because it may not recognize the deassertion of RTS until after it has begun sending the additional byte. RTS

is automatically reasserted once the RCV FIFO is emptied by reading the receiver-buffer register.

When the trigger level is 14 (see Figure 23), RTS is deasserted after the first data bit of the 16th character is

present on the SIN line. RTS is reasserted when the RCV FIFO has at least one available byte space.

auto-CTS (see Figure 20)

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 currently being sent (see Figure 21). 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.

enabling autoflow control and auto-CTS

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 an external control signal is driving CTS).

TL16C554APNR Datasheet(PDF) 33 Page - Texas Instruments

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