xr16c2852ij Exar Corporation, xr16c2852ij Datasheet - Page 15

• Manufacturer Part Number: xr16c2852ij
• Description: 2.97v To 5.5v Dual Uart With 128-byte Fifos
• Manufacturer: Exar Corporation

xr
REV. 2.1.1
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
•
•
With the Auto RTS function enabled, the RTS# output pin will not be de-asserted (logic 1) when the receive
FIFO reaches the programmed trigger level, but will be de-asserted when the FIFO reaches the next trigger
level
level below the programmed trigger level. However, even under these conditions, the 2852 will continue to
accept data until the receive FIFO is full if the remote UART transmitter continues to send data.
•
The 2852 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 2852 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).
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.
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
•
With the Auto CTS 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# input is
re-asserted (logic 0), indicating more data may be sent.
•
2.13
2.14
2.15
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).
Enable RTS interrupt through IER bit-6 (after setting EFR bit-4). The UART issues an interrupt when the
RTS# pin is de-asserted (LOW) during Auto RTS flow control mode: ISR bit-5 will be set to logic 1.
Enable auto CTS flow control using EFR bit-7.
Enable CTS interrupt through IER bit-7 (after setting EFR bit-4). The UART issues an interrupt when the
CTS# pin is de-asserted (logic 1) during Auto CTS flow control mode: ISR bit-5 will be set to 1.
(See Table
Auto RTS (Hardware) Flow Control
Auto CTS Flow Control
Auto RTS Hysteresis
10). The RTS# output pin will be asserted again after the FIFO is unloaded to the next trigger
Figure
11):
15
2.97V TO 5.5V DUAL UART WITH 128-BYTE FIFOS
Figure
11):
Table 13
shows the complete
XR16C2852