xr16v2751im Exar Corporation, xr16v2751im Datasheet - Page 17

• Manufacturer Part Number: xr16v2751im
• Description: High Performance Duart With 64-byte Fifo And Powersave Feature
• Manufacturer: Exar Corporation

REV. 1.0.1
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
•
If using the Auto CTS interrupt:
•
F
2.15
IGURE
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 (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.
The local UART (UARTA) starts data transfer by asserting RTSA# (1). RTSA# is normally connected to CTSB# (2) of
remote UART (UARTB). CTSB# allows its transmitter to send data (3). TXB data arrives and fills UARTA receive FIFO
(4). When RXA data fills up to its receive FIFO trigger level, UARTA activates its RXA data ready interrupt (5) and con-
tinues to receive and put data into its FIFO. If interrupt service latency is long and data is not being unloaded, UARTA
monitors its receive data fill level to match the upper threshold of RTS delay and de-assert RTSA# (6). CTSB# follows
(7) and request UARTB transmitter to suspend data transfer. UARTB stops or finishes sending the data bits in its trans-
mit shift register (8). When receive FIFO data in UARTA is unloaded to match the lower threshold of RTS delay (9),
UARTA re-asserts RTSA# (10), CTSB# recognizes the change (11) and restarts its transmitter and data flow again until
next receive FIFO trigger (12). This same event applies to the reverse direction when UARTA sends data to UARTB
with RTSB# and CTSA# controlling the data flow.
10. A
Auto CTS Flow Control
UTO
(RXA FIFO
CTSB#
RXA FIFO
Interrupt)
RTSA#
TXB
INTA
Trigger Reached
RTS
Receiver FIFO
Trigger Level
Local UART
Transmitter
Auto CTS
Auto RTS
UARTA
Monitor
HIGH PERFORMANCE DUART WITH 64-BYTE FIFO AND POWERSAVE FEATURE
AND
Data Starts
Receive
Data
CTS F
Figure
Assert RTS# to Begin
1
2
Transmission
Trigger Level
3
4
LOW
RX FIFO
10):
RTSA#
TXA
CTSA#
RXA
ON
C
ON
ONTROL
5
O
7
Threshold
RTS High
PERATION
17
6
8
OFF
Suspend
OFF
RTSB#
CTSB#
RTS Low
Threshold
RXB
TXB
Restart
9
10
11
Trigger Reached
Remote UART
ON
Trigger Level
Receiver FIFO
12
Auto CTS
Transmitter
Auto RTS
UARTB
Monitor
ON
Trigger Level
RX FIFO
RTSCTS1
XR16V2751