XR16M2750IM48-F Datasheet, PDF (16/53 Pages) Exar Corporation – 1.62V TO 3.63V HIGH PERFORMANCE DUART WITH 64-BYTE FIFO

XR16M2750
1.62V TO 3.63V HIGH PERFORMANCE DUART WITH 64-BYTE FIFO
REV. 1.0.0
2.12 Auto RTS (Hardware) Flow Control
Automatic RTS hardware flow control is used to prevent data overrun to the local receiver FIFO. The RTS#
output is used to request remote unit to suspend/resume data transmission. The auto RTS flow control
features is enabled to fit specific application requirement (see Figure 10):
• Enable auto RTS flow control using EFR bit-6.
• The auto RTS function must be started by asserting RTS# output pin (MCR bit-1 to logic 1 after it is enabled).
If using the Auto RTS interrupt:
• Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin makes a transition from low to high: ISR bit-5 will be set to logic 1.
2.13 Auto RTS Hysteresis
The M2750 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the XR16C850, ST16C650A and ST16C550 family of UARTs. With the Auto RTS function enabled, an interrupt
is generated when the receive FIFO reaches the programmed RX trigger level. The RTS# pin will not be forced
HIGH (RTS off) until the receive FIFO reaches the upper limit of the hysteresis level. The RTS# pin will return
LOW after the RX FIFO is unloaded to the lower limit of the hysteresis level. Under the above described
conditions, the M2750 will continue to accept data until the receive FIFO gets full. The Auto RTS function is
initiated when the RTS# output pin is asserted LOW (RTS On). Table 13 shows the complete details for the
Auto RTS# Hysteresis levels. Please note that this table is for programmable trigger levels only (Table D). The
hysteresis values for Tables A-C are the next higher and next lower trigger levels in the corresponding table.
2.14 Auto CTS Flow Control
Automatic CTS flow control is used to prevent data overrun to the remote receiver FIFO. The CTS# input is
monitored to suspend/restart the local transmitter. The auto CTS flow control feature is selected to fit specific
application requirement (see Figure 10):
• Enable auto CTS flow control using EFR bit-7.
If using the Auto CTS interrupt:
• Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (HIGH): ISR bit-5 will be set to 1, and UART will suspend transmission as soon as
the stop bit of the character in process is shifted out. Transmission is resumed after the CTS# input is re-
asserted (LOW), indicating more data may be sent.
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