XR17V254 Datasheet, PDF (43/70 Pages) Exar Corporation – 66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT

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XR17V254
66MHZ PCI BUS QUAD UART WITH POWER MANAGEMENT SUPPORT
TABLE 15: INTERRUPT SOURCE AND PRIORITY LEVEL
PRIORITY
ISR REGISTER STATUS BITS
SOURCE OF THE INTERRUPT
LEVEL BIT [5] BIT [4] BIT [3] BIT [2] BIT [1] BIT [0]
1
0
0
0
1
1
0 LSR (Receiver Line Status Register)
2
0
0
0
1
0
0 RXRDY (Received Data Ready)
3
0
0
1
1
0
0 RXRDY (Receive Data Time-out)
4
0
0
0
0
1
0 TXRDY (Transmitter Holding Register Empty)
5
0
0
0
0
0
0 MSR (Modem Status Register)
6
0
1
0
0
0
0 RXRDY (Received Xon/Xoff or Special character)
7
1
0
0
0
0
0 CTS#/DSR#, RTS#/DTR# change of state
X
0
0
0
0
0
1 None (default)
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.
ISR[5:1]: Interrupt Status
These bits indicate the source for a pending interrupt at interrupt priority levels (See Table 15). See “Section
5.5.1, Interrupt Generation:” on page 42 and “Section 5.5.2, Interrupt Clearing:” on page 42 for details.
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).
5.6 FIFO Control Register (FCR) - Write Only
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[7:6]: Receive FIFO Trigger Select
(logic 0 = default, RX trigger level =1)
The FCTR bits [5:4] are associated with these 2 bits. These 2 bits are used to set the trigger level for the
receive FIFO. The UART will issue a receive interrupt when the number of the characters in the FIFO crosses
the trigger level. Table 16 shows the complete selections. Note that the receiver and the transmitter cannot use
different trigger tables. Whichever selection is made last applies to both the RX and TX side.
FCR[5:4]: Transmit FIFO Trigger Select (requires EFR bit [4]=1)
(logic 0 = default, TX trigger level = 1)
The FCTR bits [7:6] are associated with these 2 bits by selecting one of the four tables. The 4 user selectable
trigger levels in 4 tables are supported for compatibility reasons. These 2 bits set the trigger level for the
transmit FIFO interrupt. The UART will issue a transmit interrupt when the number of characters in the FIFO
falls below the selected trigger level, or when it gets empty in case that the FIFO did not get filled over the
trigger level on last re-load. Table 16 below shows the selections.
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