Difference between revisions of "QBUS backplanes"
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It is usually possible to upgrade 18-bit backplanes to 22-bit; see [[Upgrading QBUS backplanes]]. | It is usually possible to upgrade 18-bit backplanes to 22-bit; see [[Upgrading QBUS backplanes]]. | ||
| − | '''''NOTE WELL:''''' For reasons which seem utterly incomprehensible, many boards designed for Q/CD slots (such as [[Private Memory Interconnect|PMI]] cards) '''do not''' avoid the QBUS pins on the CD connectors which contain 'hazardous' (to TTL circuitry) voltages. | + | '''''NOTE WELL:''''' For reasons which seem utterly incomprehensible, many boards designed for Q/CD slots (such as [[Private Memory Interconnect|PMI]] cards) '''do not''' avoid the QBUS pins on the CD connectors which contain 'hazardous' (to TTL circuitry) voltages. [''NOTE:'' The exact failure mode here is still not understood; the PMI spec was examined, but no clash of pin assignments was found. The warning is accurate, though: [http://web.frainresearch.org:8080/projects/pdp-11/micronotes/micronote28.txt MicroNote 28] says "MSV11-J MODULES CAN[NOT] BE PLACED IN A Q/Q BACKPLANE SLOT. IF THIS IS ATTEMPTED PERMANENT DAMAGE WILL BE DONE TO THE BOARDS".] So, plugging such a card into a Q/Q backplane will generally '''''destroy''''' the card. |
==Backplane types== | ==Backplane types== | ||
Revision as of 14:16, 21 October 2021
QBUS backplanes come mainly in two physical types, dual-width and quad-width. In the quad-width backplanes, each slot held four 'connectors', DEC's term for a group of edge connector pins, denominated 'A'-'D'.
The QBUS itself is fully carried in a dual slot, and the quads are further sub-divided into two types, the so-called Q/Q and Q/CD. In quad Q/Q units, both sides of each quad slot are fully wired for QBUS, and so a single slot can hold two separate dual-width QBUS devices. The device locations are usually arranged for grant priority in so-called 'serpentine' order, i.e. one with the devices in the following kind of order (facing the backplane from the board side):
1-2
4-3
5-6
8-7
9-10
etc.
In a quad Q/CD backplane, the CD connectors form a private bus, sometimes called the CD interconnect, used to connect together board pairs. (The CD connectors run down the right-hand side, when facing the side of the backplane where the boards plug in, with the CPU at the top.)
It is usually possible to upgrade 18-bit backplanes to 22-bit; see Upgrading QBUS backplanes.
NOTE WELL: For reasons which seem utterly incomprehensible, many boards designed for Q/CD slots (such as PMI cards) do not avoid the QBUS pins on the CD connectors which contain 'hazardous' (to TTL circuitry) voltages. [NOTE: The exact failure mode here is still not understood; the PMI spec was examined, but no clash of pin assignments was found. The warning is accurate, though: MicroNote 28 says "MSV11-J MODULES CAN[NOT] BE PLACED IN A Q/Q BACKPLANE SLOT. IF THIS IS ATTEMPTED PERMANENT DAMAGE WILL BE DONE TO THE BOARDS".] So, plugging such a card into a Q/Q backplane will generally destroy the card.
Backplane types
The following table lists the backplanes produced by DEC:
| ID | Type | Height | Address Width | Chassis | Termination | Comments |
|---|---|---|---|---|---|---|
| H9270-A | Q/Q | 4 | Q18 | BA11-M | none | |
| H9270-Q | Q/Q | 4 | Q18/Q22 | none | ||
| H9273 | Q/CD | 9 | Q18 | BA11-N | none | |
| H9275 | Q/Q | 9 | Q22 | 120 ohms | ||
| H9276 | Q/CD | 9 | Q22 | BA11-S | none | |
| H9278 | mixed | 8 | Q22 | BA23 | none | slots 1-3 are Q/CD; slots 4-8 are Q/Q |
| H9281-Q | Q | 4/8/12 | Q18/Q22 | none/120 ohms | ||
| DDV11-B | hex Q/Q | 9 | Q18 | H909-C | none | E-F connectors un-wired |
'Type' indicates whether it is dual-width ('Q') or quad. 'Height' is the number of slots; the number of dual-width board which can be plugged in is twice this, for Q/Q quad backplanes.
