TL16C550C, TL16C550CI

ASYNCHRONOUS COMMUNICATIONS ELEMENT

WITH AUTOFLOW CONTROL

SLLS177F – MARCH 1994 – REVISED MARCH 2001

4

POST OFFICE BOX 655303

auto-CTS and auto-RTS functional timing

Start

Bits 0 – 7

Start

Bits 0 – 7

Start

Bits 0 – 7

Stop

Stop

Stop

SOUT

CTS

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

B. If 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 Waveforms

The receiver FIFO trigger level can be set to 1, 4, 8, or 14 bytes. These are described in Figures 3 and 4.

Start

Byte N

Start

Byte N+1

Start

Byte

Stop

Stop

Stop

SIN

RTS

RD

(RD RBR)

12

N

N+1

NOTES: A. N = RCV FIFO trigger level (1, 4, or 8 bytes)

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

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

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

NOTES: A. RTS is deasserted when the receiver receives the first data bit of the sixteenth byte. The receive FIFO is full after finishing the

sixteenth byte.

B. RTS is asserted again when there is at least one byte of space available and no incoming byte is in processing or there is more than

one byte of space available.

C. When the receive FIFO is full, the first receive buffer register read reasserts RTS.

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