TL16C752D Datasheet, PDF (17/56 Pages) Texas Instruments – TL16C752D Dual UART With 64-Byte FIFO

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TL16C752D
SLLSEN8B – SEPTEMBER 2015 – REVISED MARCH 2016
Feature Description (continued)
8.3.1.2 Hardware Flow Control
Hardware flow control is composed of auto-CTS and auto-RTS. Auto-CTS and auto-RTS can be enabled or
disabled independently by programming EFR[7:6].
With auto-CTS, CTS must be active before the UART can transmit data. Auto-RTS only activates the RTS output
when there is enough room in the FIFO to receive data and deactivates the RTS output when the RX FIFO is
sufficiently full. The HALT and RESTORE trigger levels in the TCR determine the levels at which RTS is
activated or deactivated. If both auto-CTS and auto-RTS are enabled, when RTS is connected to CTS, data
transmission does not occur unless the receiver FIFO has empty space. Thus, overrun errors are eliminated
during hardware flow control. If not enabled, overrun errors occur if the transmit data rate exceeds the receive
FIFO servicing latency.
8.3.1.3 Auto-RTS
Auto-RTS data flow control originates in the receiver block (see Figure 14). Figure 16 shows RTS functional
timing. The receiver FIFO trigger levels used in Auto-RTS are stored in the TCR. RTS is active if the RX FIFO
level is below the HALT trigger level in TCR[3:0]. When the receiver FIFO HALT trigger level is reached, RTS is
deasserted. The sending device (for example, another UART) may send an additional byte after the trigger level
is reached (assuming the sending UART has another byte to send) because it may not recognize the deassertion
of RTS until it has begun sending the additional byte. RTS is automatically reasserted once the receiver FIFO
reaches the RESUME trigger level programmed via TCR[7:4]. This reassertion allows the sending device to
resume transmission.
RX
Start Byte N Stop
Start Byte N+1 Stop
Start
RTS
IOR
1
2
N
N+1
A. N = receiver FIFO trigger level B.
B. The two blocks in dashed lines cover the case where an additional byte is sent as described in Auto-RTS.
Figure 16. RTS Functional Timing
8.3.1.4 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 17 shows CTS functional timing, and Figure 18
shows an example of autoflow control.
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