TL16C754 Datasheet, PDF (7/39 Pages) Texas Instruments – QUAD UART WITH 64-BYTE FIFO

TL16C754
QUAD UART WITH 64-BYTE FIFO
SLLS279A – OCTOBER 1998 – REVISED OCTOBER 1999
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
UART 2
D7–D0
RX
FIFO
Serial to
Parallel
RX TX
Parallel to
Serial
Flow
Control
RTS CTS
Flow
Control
TX
FIFO
TX
FIFO
Parallel to
Serial
TX RX
Serial to
Parallel
Flow
Control
CTS RTS
Flow
Control
RX
FIFO
D7–D0
Figure 3. Autoflow Control (Auto-RTS and Auto-CTS) Example
software flow control
Software flow control is enabled through the enhanced feature register and the modem control register. Different
combinations of software flow control can be enabled by setting different combinations of EFR[3–0]. Table 1
shows software flow control options.
There are two other enhanced features relating to S/W flow control:
– Xon Any Function [MCR(5): Operation will resume after receiving any character after recognizing the
Xoff character.
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