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VMEchip2
Programming the Local Bus Interrupter
2
2-77
2VMEchip2
LCSR Programming Model
The local bus interrupter is used by devices that wish to interrupt
the local bus. There are 31 devices that can interrupt the local bus
through the VMEchip2. In the general case, each interrupter has a
level select register, an enable bit, a status bit, a clear bit, and for the
software interrupts, a set bit. Each interrupter also provides a
unique interrupt vector to the processor. The upper four bits of the
vector are programmable in the vector base registers. The lower
four bits are unique for each interrupter. There are two base
registers, one for the first 16 interrupters, and one for the next 8
interrupters. The VMEbus interrupters provide their own vectors.
A summary of the interrupts is shown in Table 2-3.
The status bit of an interrupter is affected by the enable bit. If the
enable bit is low, the status bit is also low. Interrupts may be polled
by setting the enable bit and programming the level to zero. This
enables the status bit and prevents the local bus from being
interrupted. The enable bit does not clear edge-sensitive interrupts.
If necessary, edge-sensitive interrupts should be cleared, in order to
remove any old interrupts, and then enabled. The master interrupt
enable (MIEN) bit must be set before the VMEchip2 can generate
any interrupts. The MIEN bit is in the I/O Control Register 1.
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