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Chapter 6
Multiple MXIbus devices can interrupt on the same interrupt line; therefore, a MXIbus interrupt
acknowledge daisy-chain is required. The MXIbus GIN and GOUT signals are normally used
for the arbitration bus grant in/bus grant out daisy-chain. However, when a MXIbus device
initiates a MXIbus IACK cycle and drives the MXIbus address modifier code hex 12, the
MXIbus GIN and GOUT lines are used as the interrupt acknowledge daisy-chain. The MXIbus
System Controller starts the interrupt acknowledge daisy-chain when it detects the address
modifier code hex 12. The interrupt acknowledge signal propagates down the daisy-chain to
each MXIbus device. If the device is not interrupting the MXIbus, it passes the signal down the
daisy-chain to the next device. If the MXIbus device is interrupting, the cycle is converted into a
VMEbus IACK cycle.
A MXIbus device not capable of generating a MXIbus IACK cycle can service an interrupt in a
remote VXIbus mainframe by reading from a designated address in the MXIbus configuration
space on the remote VXI-MXI. The external device must know which VMEbus interrupt level it
is servicing and read from the appropriate address. Table 6-1 shows the designated addresses for
VMEbus IRQ[7–1].
Table 6-1. VXI-MXI Addresses for VMEbus Interrupt Levels
VMEbus IRQ Line
VMEbus IRQ1
VMEbus IRQ2
VMEbus IRQ3
VMEbus IRQ4
VMEbus IRQ5
VMEbus IRQ6
VMEbus IRQ7
Reading from one of the addresses listed in Table 6-1 initiates a VMEbus IACK cycle. The
information sent back from the read is the VXIbus Status/ID information defined in the VXIbus
specification. The lower byte of the Status/ID is the logical address of the responding
interrupter. The upper byte is user defined.
When one of the local VXI-MXI interrupt conditions is serviced by an interrupt handler, the
Status/ID information returned is as follows:
15
14
LINT3
LINT2
7
6
LADD7
LADD6
© National Instruments Corporation
VXI-MXI Configuration Register to Read
Interrupt Acknowledge 1 (VXI-MXI offset = 32)
Interrupt Acknowledge 2 (VXI-MXI offset = 34)
Interrupt Acknowledge 3 (VXI-MXI offset = 36)
Interrupt Acknowledge 4 (VXI-MXI offset = 38)
Interrupt Acknowledge 5 (VXI-MXI offset = 3A)
Interrupt Acknowledge 6 (VXI-MXI offset = 3C)
Interrupt Acknowledge 7 (VXI-MXI offset = 3E)
13
12
LINT1
ACFAILINT
5
4
LADD5
LADD4
11
10
BKOFF
TRIGINT
3
2
LADD3
LADD2
6-5
Theory of Operation
9
8
SYSFAIL
ACFAIL
1
0
LADD0
LADD1
VXI-MXI User Manual
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