Non-Processor Request

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A Non-Processor Request is one of the two kinds of bus requests on the UNIBUS; it is used exclusively to gain control of the UNIBUS's data section so that the device may perform a DMA cycle.

The name comes from the fact that the device cannot request that the CPU perform any action (i.e. an interrupt) while the device has control of the bus.

A device gaining control of the UNIBUS via an NPR request may perform more than one master-slave cycle before relinquishing control of the bus, however.