Chapter 4
Register Descriptions
© National Instruments Corporation
4-33
VME-MXI-2 User Manual
VMEbus Interrupt Status Register (VISTR)
VMEbus A16 Offset:
2A (hex)
Attributes:
Read Only
16, 8-bit accessible
15
14
13
12
11
10
9
8
LINT[3]
LINT[2]
LINT[1]
AFINT
BKOFF
0
SYSFAIL
ACFAIL
7
6
5
4
3
2
1
0
SFINT
IRQ[7]
IRQ[6]
IRQ[5]
IRQ[4]
IRQ[3]
IRQ[2]
IRQ[1]
You can use this register to monitor the VMEbus IRQ[7:1] lines and the status of local
VME-MXI-2 interrupt conditions. Bits 15 through 8 of this register, along with the
logical address of the VME-MXI-2 on bits 7 through 0, are returned during an interrupt
acknowledge cycle for the local interrupt condition.
Bit
Mnemonic
Description
15-13
LINT[3:1]
Local Interrupt Level
These bits reflect the state of the LINT[3:1] bits
in the VMEbus Interrupt Control Register
(VICTR).
12
AFINT
VMEbus ACFAIL* Interrupt Status
This bit returns 1 when the VME-MXI-2 is
driving the VMEbus IRQ[7:1] selected by
LINT[3:1] because the ACFAIL* line is
asserted. This bit clears after the VME-MXI-2
responds to an interrupt acknowledge cycle for
the local interrupt. The ACFAIL* interrupt is
enabled with the AFIE bit in the VMEbus
Interrupt Control Register (VICTR).
11
BKOFF
Back Off Status
This bit is set when the VME-MXI-2 encounters
a deadlock condition between the VMEbus and
the MXIbus. If the BKOFFIE bit in the VMEbus
Interrupt Control Register (VICTR) is set, an
interrupt is also generated. This bit stores the
deadlock status even when the interrupt is not
enabled. This bit clears when read either directly
or through an interrupt acknowledge cycle.
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