XR19L210 Datasheet, PDF (12/43 Pages) Exar Corporation – SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER

XR19L210
PRELIMINARY
SINGLE CHANNEL INTEGRATED UART AND RS-232 TRANSCEIVER
REV. P1.0.2
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 L210 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 de-asserted until the receive FIFO reaches
one trigger level above the programmed trigger level in the trigger table (Table 8). The RTS pin will be re-
asserted after the RX FIFO is unloaded to one trigger level lower than the programmed trigger level. This is
described in Figure 10. Under the above described conditions, the L210 will continue to accept data until the
receive FIFO gets full. The Auto RTS function is initiated when the RTS output pin is asserted.
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: 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, indicating
more data may be sent.
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