XR16V798_08 Datasheet, PDF (15/56 Pages) Exar Corporation – HIGH PERFORMANCE 2.25V TO 3.6V OCTAL UART WITH FRACTIONAL

XR16V798
REV. 1.0.1
HIGH PERFORMANCE 2.25V TO 3.6V OCTAL UART WITH FRACTIONAL BAUD RATE
2.10 Auto RTS/DTR Hardware Flow Control Operation
Automatic RTS/DTR flow control is used to prevent data overrun to the local receiver FIFO. The RTS#/DTR#
output pin is used to request remote unit to suspend/resume data transmission. The flow control features are
individually selected to fit specific application requirement (see Figure 9):
• Select RTS (and CTS) or DTR (and DSR) through MCR bit-2.
• Enable auto RTS/DTR flow control using EFR bit-6.
• The auto RTS or auto DTR function must be started by asserting the RTS# or DTR# output pin (MCR bit-1 or
bit-0 to a logic 1, respectively) after it is enabled.
• If using programmable RX FIFO trigger levels, hysteresis levels can be selected via FCTR bits 3-0.
With the Auto RTS function enabled, the RTS# output pin will not be de-asserted (HIGH) when the receive
FIFO reaches the programmed trigger level, but will be de-asserted when the FIFO reaches the next trigger
level for Trigger Tables A-C (See Table 14). The RTS# output pin will be asserted (LOW) again after the FIFO
is unloaded to the next trigger level below the programmed trigger level.
For Trigger Table D (or programmable trigger levels), the RTS# output pin is de-asserted when the the RX
FIFO level reaches the RX trigger level plus the hysteresis level and is asserted when the RX FIFO level falls
below the RX trigger level minus the hysteresis level.
However, even under these conditions, the 798 will continue to accept data until the receive FIFO is full if the
remote UART transmitter continues to send data.
• If used, enable RTS/DTR interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt
when the RTS#/DTR# pin makes a transition: ISR bit-5 will be set to 1.
2.10.1 Auto CTS/DSR Flow Control
Automatic CTS/DSR flow control is used to prevent data overrun to the remote receiver FIFO. The CTS/DSR
pin is monitored to suspend/restart local transmitter. The flow control features are individually selected to fit
specific application requirement (see Figure 9):
• Select CTS (and RTS) or DSR (and DTR) through MCR bit-2.
• Enable auto CTS/DSR flow control using EFR bit-7.
With the Auto CTS or Auto DTR function enabled, the UART will suspend transmission as soon as the stop bit
of the character in the Transmit Shift Register has been shifted out. Transmission is resumed after the CTS#/
DTR# input is re-asserted (LOW), indicating more data may be sent.
• If used, enable CTS/DSR interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt
when the CTS#/DSR# pin makes a transition: ISR bit-5 will be set to a logic 1, and UART will suspend TX
transmissions as soon as the stop bit of the character in process is shifted out. Transmission is resumed
after the CTS#/DSR# input returns LOW, indicating more data may be sent.
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