XR17D154 Exar Corporation, XR17D154 Datasheet - Page 26

• Manufacturer Part Number: XR17D154
• Description: Four-channel Pci-bus Uart
• Manufacturer: Exar Corporation

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PRELIMINARY
F
IGURE
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.
11. A
(RXA FIFO
CTSB#
RXA FIFO
Interrupt)
RTSA#
TXB
INTA
Trigger Reached
UTO
Receiver FIFO
Trigger Level
Local UART
Transmitter
Auto CTS
Auto RTS
UARTA
Monitor
RTS/DTR
Data Starts
Receive
Data
Assert RTS# to Begin
1
AND
2
Transmission
Trigger Level
3
4
RX FIFO
CTS/DSR F
RTSA#
TXA
CTSA#
RXA
ON
ON
LOW
5
C
7
Threshold
RTS High
ONTROL
26
6
8
UNIVERSAL (3.3V AND 5V) PCI BUS QUAD UART
OFF
Suspend
O
OFF
PERATION
RTSB#
CTSB#
RTS Low
Threshold
RXB
TXB
Restart
9
10
11
Trigger Reached
ON
Remote UART
Trigger Level
Receiver FIFO
12
Auto CTS
Transmitter
Auto RTS
UARTB
Monitor
ON
Trigger Level
RX FIFO
R T S C T S 1
XR17D154
REV. P1.0.0