TL16C550C, TL16C550CI
ASYNCHRONOUS COMMUNICATIONS ELEMENT
WITH AUTOFLOW CONTROL
SLLS177E – MARCH 1994 – REVISED APRIL1998
auto-CTS and auto-RTS functional timing
SOUT
Start
Bits 0 – 7
Stop
Start
Bits 0 – 7 Stop
Start
Bits 0 – 7 Stop
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.
SIN
Start
Byte N
Stop
Start
Byte N+1
Stop
Start
Byte
Stop
RTS
RD
(RD RBR)
1
2
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
SIN
Byte 14
Byte 15
Start
Byte 16
Stop
Start
Byte 18 Stop
RTS
RTS Released After the
First Data Bit of Byte 16
RD
(RD RBR)
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
4
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