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:'' 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: [ | + | '''''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: [https://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/hardware/micronotes/numerical/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== | ||
+ | |||
+ | Several manufacturers produced QBus compatible backplanes: | ||
+ | |||
+ | ===DEC Backplanes=== | ||
The following table lists the backplanes produced by [[Digital Equipment Corporation|DEC]]: | The following table lists the backplanes produced by [[Digital Equipment Corporation|DEC]]: | ||
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| [[H9276 backplane|H9276]] || Q/CD || 9 || Q22 || [[BA11-S mounting box|BA11-S]] || none | | [[H9276 backplane|H9276]] || Q/CD || 9 || Q22 || [[BA11-S mounting box|BA11-S]] || none | ||
|- | |- | ||
− | | [[H9278 backplane|H9278]] || mixed || 8 || Q22 || [[BA23]] || none || slots 1-3 are Q/CD; slots 4-8 are Q/Q | + | | [[H9278 backplane|H9278]] || mixed || 8 || Q22 || [[BA23]] || none || slots 1-3 are Q/CD; slots 4-8 are Q/Q; removable termination packs |
|- | |- | ||
| [[54-17507 backplane|54-17507]] || mixed || 12+1 || Q22 || [[BA123]] || 120 ohms || slots 1-4 are Q/CD; slots 5-12 are Q/Q;<br>slot 13 provides only power and the [[DCOK Signal]] | | [[54-17507 backplane|54-17507]] || mixed || 12+1 || Q22 || [[BA123]] || 120 ohms || slots 1-4 are Q/CD; slots 5-12 are Q/Q;<br>slot 13 provides only power and the [[DCOK Signal]] | ||
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The DDV11-C details are somewhat speculative; in the [[VS11 Graphic System|VS11]], it is used with a [[VSV11 Graphic System|VSV11]], and the VSV11's Video Bus is carried over the E-F connectors. Puzzlingly, the VS11 documentation shows that a DDV11-D may also be used - but it claims to have the E-F connectors un-wired. | The DDV11-C details are somewhat speculative; in the [[VS11 Graphic System|VS11]], it is used with a [[VSV11 Graphic System|VSV11]], and the VSV11's Video Bus is carried over the E-F connectors. Puzzlingly, the VS11 documentation shows that a DDV11-D may also be used - but it claims to have the E-F connectors un-wired. | ||
+ | |||
+ | ===MDB Backplanes=== | ||
+ | |||
+ | [[MDB Systems]] produced many third-party QBus options, including backplanes and complete chassis systems: | ||
+ | |||
+ | {| class="wikitable" | ||
+ | ! ID !! Type !! Width || Address Width !! Assembly || Chassis !! Termination || Comments | ||
+ | |- | ||
+ | | [[40328]] || Q/Q || 8 || Q18 || [[MLSI-BPA84]] || [[MLSI-BA11-200]] || none || Wire wrap pins, can be wrapped to Q22 | ||
+ | |} | ||
+ | |||
+ | 'Type' indicates slot height and wiring, a value with a slash indicates quad height slots. 'Width' is the number of slots; if the backplane is quad-height, twice as many dual-height modules will fit. | ||
+ | |||
+ | As with DEC backplanes, MDB backplanes that are Q/Q will damage QBus cards with CD interconnects. | ||
==External links== | ==External links== | ||
* [http://www.bitsavers.org/pdf/dec/qbus/Digital_Microcomputer_Products_Handbook_1985.pdf Microcomputer Products Handbook (19850] - backplanes are covered in Part X, 'Backplanes, Enclosures, and Expansion Cables' | * [http://www.bitsavers.org/pdf/dec/qbus/Digital_Microcomputer_Products_Handbook_1985.pdf Microcomputer Products Handbook (19850] - backplanes are covered in Part X, 'Backplanes, Enclosures, and Expansion Cables' | ||
− | * [ | + | * [https://www.ibiblio.org/pub/academic/computer-science/history/pdp-11/hardware/micronotes/numerical/micronote29.txt Q-bus Expansion Concepts] ([[MicroNote]] #029) |
* [http://www.douglaspcb.com/ Douglas Electronics] still sells extender cards for DEC backplanes | * [http://www.douglaspcb.com/ Douglas Electronics] still sells extender cards for DEC backplanes | ||
** [https://www.douglaspcb.com/index.php/6-de-11.html 6-DE-11-C dual extender] | ** [https://www.douglaspcb.com/index.php/6-de-11.html 6-DE-11-C dual extender] |
Revision as of 20:33, 24 July 2024
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 (as shown here).
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
Several manufacturers produced QBus compatible backplanes:
DEC Backplanes
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; removable termination packs |
54-17507 | mixed | 12+1 | Q22 | BA123 | 120 ohms | slots 1-4 are Q/CD; slots 5-12 are Q/Q; slot 13 provides only power and the DCOK Signal |
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 |
DDV11-C | hex Q/Q | 4 | Q18 | none | E-F connectors wired as CD interconnect |
'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.
The DDV11-C details are somewhat speculative; in the VS11, it is used with a VSV11, and the VSV11's Video Bus is carried over the E-F connectors. Puzzlingly, the VS11 documentation shows that a DDV11-D may also be used - but it claims to have the E-F connectors un-wired.
MDB Backplanes
MDB Systems produced many third-party QBus options, including backplanes and complete chassis systems:
ID | Type | Width | Address Width | Assembly | Chassis | Termination | Comments |
---|---|---|---|---|---|---|---|
40328 | Q/Q | 8 | Q18 | MLSI-BPA84 | MLSI-BA11-200 | none | Wire wrap pins, can be wrapped to Q22 |
'Type' indicates slot height and wiring, a value with a slash indicates quad height slots. 'Width' is the number of slots; if the backplane is quad-height, twice as many dual-height modules will fit.
As with DEC backplanes, MDB backplanes that are Q/Q will damage QBus cards with CD interconnects.
External links
- Microcomputer Products Handbook (19850 - backplanes are covered in Part X, 'Backplanes, Enclosures, and Expansion Cables'
- Q-bus Expansion Concepts (MicroNote #029)
- Douglas Electronics still sells extender cards for DEC backplanes