Difference between revisions of "UNIBUS priority plug"
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| − | A '''UNIBUS priority plug''' is an insertable plug, physically a [[Dual Inline Package|DIP]], which was inserted into almost all [[UNIBUS]] [[peripheral|devices]] in order to select which daisy-chained [[interrupt]] [[bus grant]] | + | A '''UNIBUS priority plug''' is an insertable plug, physically a [[Dual Inline Package|DIP]], which was inserted into almost all [[UNIBUS]] [[peripheral|devices]] in order to select which daisy-chained [[interrupt]] [[bus grant line]], of the four such available on the UNIBUS (BG4, BG5, BG6, and BG7), the device's [[Bus Arbitration on the Unibus and QBUS|grant-acquiring/passing circuitry]] was connected to. As a secondary purpose, it passed all the other grant lines past the device. |
As part of the configuration of a device being added to a system, it was necessary to ensure that a priority plug for the desired priority level was installed in the device. | As part of the configuration of a device being added to a system, it was necessary to ensure that a priority plug for the desired priority level was installed in the device. | ||
Revision as of 19:38, 22 February 2024
A UNIBUS priority plug is an insertable plug, physically a DIP, which was inserted into almost all UNIBUS devices in order to select which daisy-chained interrupt bus grant line, of the four such available on the UNIBUS (BG4, BG5, BG6, and BG7), the device's grant-acquiring/passing circuitry was connected to. As a secondary purpose, it passed all the other grant lines past the device.
As part of the configuration of a device being added to a system, it was necessary to ensure that a priority plug for the desired priority level was installed in the device.
Priority plugs were manufactured by DEC for all four priority levels:
| Level | DEC part number |
|---|---|
| 4 | |
| 5 | 54-08778 |
| 6 | |
| 7 |
Most devices also came with a plug pre-installed at manufacturing time, at a level selected by DEC as likely the most appropriate interrupt priority level for that device; they were rarely changed.
