XR17D158 Exar Corporation, XR17D158 Datasheet - Page 40

• Manufacturer Part Number: XR17D158
• Description: Eight-channel Pci-bus Uart
• Manufacturer: Exar Corporation

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PRELIMINARY
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ISR[0]: Interrupt Status
Logic 0 = An interrupt is pending and the ISR contents may be used as a pointer to the appropriate interrupt
service routine.
Logic 1 = No interrupt pending. (default condition)
ISR[3:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels 1, 2, 3 and 4 (See Interrupt
Source
ISR[5:4]: Interrupt Status
These bits are enabled when EFR bit-4 is set to a logic 1. ISR bit-4 indicates that the receiver detected a data
match of the Xon or Xoff character(s). Note that once set to a logic 1, the ISR bit-4 will stay a logic 1 until a Xon
character is received. ISR bit-5 indicates that CTS#/DSR# or RTS#/DTR# has changed state.
ISR[7:6]: FIFO Enable Status
These bits are set to a logic 0 when the FIFOs are disabled. They are set to a logic 1 when the FIFOs are
enabled.
FIFO CONTROL REGISTER (FCR)
This register is used to enable the FIFOs, clear the FIFOs, set the transmit/receive FIFO trigger levels, and
select the DMA mode. The DMA, and FIFO modes are defined as follows:
FCR[0]: TX and RX FIFO Enable
Logic 0 = Disable the transmit and receive FIFO (default).
Logic 1 = Enable the transmit and receive FIFOs. This bit must be set to logic 1 when other FCR bits are
written or they will not be programmed.
FCR[1]: RX FIFO Reset
This bit is only active when FCR bit-0 is active.
Logic 0 = No receive FIFO reset (default).
Logic 1 = Reset the receive FIFO pointers and FIFO level counter logic (the receive shift register is not cleared
or altered). This bit will return to a logic 0 after resetting the FIFO.
P
L
RIORITY
EVEL
X
1
2
3
4
5
6
7
Table
B
IT
12).
0
0
0
0
0
0
1
0
-5
B
IT
0
0
0
0
0
1
0
0
-4
ISR R
B
EGISTER
T
IT
0
0
1
0
0
0
0
0
ABLE
-3
12: I
B
S
IT
TATUS
1
1
1
0
0
0
0
0
-2
NTERRUPT
B
B
ITS
IT
1
0
0
1
0
0
0
0
-1
S
OURCE AND
40
UNIVERSAL (3.3V AND 5V) PCI BUS OCTAL UART
B
IT
0
0
0
0
0
0
0
1
-0
LSR (Receiver Line Status Register)
RXRDY (Received Data Ready)
RXRDY (Receive Data Time-out)
TXRDY (Transmitter Holding Register Empty)
MSR (Modem Status Register)
RXRDY (Received Xon/Xoff or Special character)
CTS#/DSR#, RTS#/DTR# change of state
None (default)
P
RIORITY
S
L
OURCE OF THE INTERRUPT
EVEL
+
XR17D158
REV. P1.0.0