TL16C550D_09 Datasheet, PDF (3/54 Pages) Texas Instruments – ASYNCHRONOUS COMMUNICATIONS ELEMENT WITH AUTOFLOW CONTROL

TL16C550D, TL16C550DI
www.ti.com .................................................................................................................................................. SLLS597E – APRIL 2004 – REVISED DECEMBER 2008
The TL16C550D is being made available in a reduced pin count package, the 24-pin ZQS package. This is
accomplished by eliminating some signals that are not required for some applications. These include the CS0,
CS1, ADS, RD2, WR2, DSR, RI, DCD, and RCLK input signals and the DDIS, TXRDY, RXRDY, OUT1, OUT2,
DTR, and BAUDOUT output signals. There is an internal connection between BAUDOUT and RCLK.
Most of the functionality of the TL16C550D is maintained in the ZQS package, except that which involves the
eliminated signals.
DETAILED DESCRIPTION
Autoflow Control (see Figure 1)
Autoflow control comprises auto-CTS and auto-RTS. With auto-CTS, the CTS input must be active before the
transmitter FIFO can emit data. With auto-RTS, RTS becomes active when the receiver needs more data and
notifies the sending serial device. When RTS is connected to CTS, data transmission does not occur unless the
receiver FIFO has space for the data; thus, overrun errors are eliminated using ACE1 and ACE2 from a
TLC16C550D with the autoflow control enabled. If not, overrun errors occur when the transmit data rate exceeds
the receiver FIFO read latency.
Figure 1. Autoflow Control (Auto-RTS and Auto-CTS) Example
Auto-RTS (see Figure 1)
Auto-RTS data flow control originates in the receiver timing and control block (see functional block diagram) and
is linked to the programmed receiver FIFO trigger level. When the receiver FIFO level reaches a trigger level of
1, 4, or 8 (see Figure 3), RTS is deasserted. With trigger levels of 1, 4, and 8, the sending ACE may send an
additional byte after the trigger level is reached (assuming the sending ACE has another byte to send) because it
may not recognize the deassertion of RTS until after it has begun sending the additional byte. RTS is
automatically reasserted once the RCV FIFO is emptied by reading the receiver buffer register.
When the trigger level is 14 (see Figure 4), RTS is deasserted after the first data bit of the 16th character is
present on the SIN line. RTS is reasserted when the RCV FIFO has at least one available byte space.
Auto-CTS (see Figure 1)
The transmitter circuitry checks CTS before sending the next data byte. When CTS is active, it sends the next
byte. To stop the transmitter from sending the following byte, CTS must be released before the middle of the last
stop bit that is currently being sent (see Figure 2). The auto-CTS function reduces interrupts to the host system.
When flow control is enabled, CTS level changes do 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 may result.
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