XR16L570 Datasheet, PDF (13/46 Pages) Exar Corporation – SMALLEST 1.62V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE

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REV. 1.0.0
XR16L570
SMALLEST 1.62V TO 5.5V UART WITH 16-BYTE FIFO AND POWERSAVE
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 11):
• 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 L570 has a new feature that provides flow control trigger hysteresis while maintaining compatibility with
the ST16C550 UART. 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 to a logic 1 (RTS off), until the
receive FIFO reaches one trigger level above the programmed trigger level in the trigger table (Table 8). The
RTS# pin will return to a logic 0 after the RX FIFO is unloaded to one trigger level lower than the programmed
trigger level. This is described in Figure 11. Under the above described conditions, the L570 will continue to
accept data until the receive FIFO gets full. The Auto RTS function is initiated when the RTS# output pin is
asserted to a logic 0 (RTS On).
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 11):
• 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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