TL16C752B
3.3-V DUAL UART WITH 64-BYTE FIFO
SLLS405A – DECEMBER 1999 – REVISED AUGUST 2000
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.
TX
Start
Byte 0–7
Stop
Start
Byte 0–7
Stop
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
UART 1
Serial to
Parallel
RX
FIFO
Flow
Control
D7–D0
Parallel to
Serial
TX
FIFO
Flow
Control
CTS RTS
Flow
Control
TX
RX
Serial to
Parallel
RX
FIFO
RTS CTS
Flow
Control
D7–D0
UART 2
RX
TX
Parallel to
Serial
TX
FIFO
Figure 3. Autoflow Control (Auto-RTS and Auto-CTS) Example
6
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