xr16m890 Exar Corporation, xr16m890 Datasheet - Page 21

• Manufacturer Part Number: xr16m890
• Description: Uart With 128-byte Fifo And Integrated Level Shifters
• Manufacturer: Exar Corporation

REV. P1.1.1
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 needed, the CTS interrupt can be enabled 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.
F
1.13
IGURE
Enable auto CTS flow control using EFR bit-7.
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.
15. 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
AND
Data Starts
Receive
Data
CTS F
Figure
Assert RTS# to Begin
1
2
Transmission
Trigger Level
3
LOW
4
RX FIFO
15):
RTSA#
TXA
CTSA#
RXA
ON
UART WITH 128-BYTE FIFO AND INTEGRATED LEVEL SHIFTERS
C
ON
ONTROL
5
PRELIMINARY
O
7
PERATION
RTS High
Threshold
21
6
8
OFF
Suspend
OFF
RTSB#
CTSB#
Threshold
RTS Low
RXB
TXB
Restart
9
10
11
Trigger Reached
ON
Remote UART
Trigger Level
Receiver FIFO
12
Auto CTS
Auto RTS
Transmitter
UARTB
Monitor
ON
Trigger Level
RX FIFO
RTSCTS1
XR16M890