Motorola MVME172 - Manual (Page 153)

http://www.mcg.mot.com/literature 2-75
2
LCSR Programming Model
2VMEchip2
LCSR Programming Model
Programming the Local Bus Interrupter
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 I/O Control Register 1.