Motorola MVME1X7P manual Programming the Local Bus Interrupter

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VMEchip2

Programming the Local Bus Interrupter

The local bus interrupter is used by devices that need 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 a set bit for the software interrupts. 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 appears in Table 2-4.

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 0. 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 re-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.

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