Non-Processor Request and Grant

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The Non-Processor Request and Non-Processor Grant (usually given as their acronyms, NPR and NPG) are the two lines on the UNIBUS used in one of the two kinds of bus requests there; they are for a device to gain control of the UNIBUS's data section so that it 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 bus via an NPR request may perform more than one master-slave cycle before relinquishing control of the bus, however.

NPR is a normal 'wired-OR' broadcast bus line; NPG is a unidirectional grant line. In an SPC, etc backplane slot, there are a pair of pins for NPG: CA1 for 'NPG In', and CB1 for 'NPG Out'. In an empty slot, or a slot holding a non-DMA device, there must be either a jumper between those pins, or a G7273 grant continuity card installed, to carry the grant across that slot.

The QBUS has a set of lines with identical functionality, DMA Request and Grant.