Difference between revisions of "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 [[conductor|lines]] on the [[UNIBUS]] used in one of the two kinds of [[bus grant|bus requests]] there; they are for a [[peripheral|device]] to gain control of the UNIBUS's data section so that it may perform a [[Direct Memory Access|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. | + | The name comes from the fact that the device cannot request that the [[Central Processing Unit|CPU]] perform any action (i.e. an [[interrupt]]) while the device has control of the [[bus]]. |
| − | A device gaining control of the | + | 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 [[bus grant line|grant line]]. In an [[Small Peripheral Controller|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 [[bus grant|grant]] across that slot. | |
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| + | The [[QBUS]] has a set of lines with identical functionality, [[DMA Request and Grant]]. | ||
[[Category: UNIBUS]] | [[Category: UNIBUS]] | ||
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Latest revision as of 17:50, 6 July 2022
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.
