Difference between revisions of "QBUS backplanes"

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(Clarify that not just aperipherls can go in QBUS slots)
 
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'''QBUS backplanes''' come mainly in two physical types, [[DEC card form factor|dual-width]] and quad-width. In the quad-width [[backplane]]s, each slot held four 'connectors', DEC's term for a [[DEC edge connector contact identification|group of edge connector pins]], denominated 'A'-'D'.
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'''QBUS backplanes''' come mostly in two physical types, [[DEC card form factor|dual-width]] and quad-width. In the quad-width [[backplane]]s, each slot held four 'connectors' (DEC's term for a group of [[DEC edge connector contact identification|edge connector pins]]), denominated 'A'-'D'.
  
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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 [[peripheral controller|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):
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The [[QBUS]] itself is fully carried in a dual slot, and the backplanes with quad slots are further sub-divided into two types, the so-called '''Q/Q''' and '''Q/CD'''. In quad Q/Q units, both sides (pairs of 'connectors') of each quad slot are fully wired for QBUS, and so a single slot can hold two separate dual-width QBUS [[peripheral controller|device]], [[main memory|memory]], etc [[printed circuit board|cards]]. The device locations are usually arranged for [[bus grant line|grant]] priority in so-called 'serpentine' order, i.e. one with the devices in the following order (facing the backplane from the board side):
  
 
1-2<br>4-3<br>5-6<br>8-7<br>9-10
 
1-2<br>4-3<br>5-6<br>8-7<br>9-10
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In a quad Q/CD backplane, the [[DEC edge connector contact identification|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.)
 
In a quad Q/CD backplane, the [[DEC edge connector contact identification|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.)
  
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It is usually possible to upgrade 18-bit backplanes to 22-bit; see [[Upgrading QBUS backplanes]].
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It is usually possible to upgrade [[QBUS#Variable address size|18-bit QBUS]] backplanes to 22-bit; see [[Upgrading QBUS backplanes]].
  
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'''''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.
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'''''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]]:
  
 
{| class="wikitable"
 
{| class="wikitable"
−
! ID !! Type !! Height || Address Width !! Chassis !! Termination || Comments
+
! ID !! Type !! # Slots || Address Width !! Chassis !! Termination || Comments
 
|-
 
|-
 
| [[H9270 backplane|H9270-A]] || Q/Q || 4  || Q18 || [[BA11-M mounting box|BA11-M]] || none
 
| [[H9270 backplane|H9270-A]] || Q/Q || 4  || Q18 || [[BA11-M mounting box|BA11-M]] || none
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|-
 
|-
 
| [[H9273 backplane|H9273]] || Q/CD || 9 || Q18 || [[BA11-N mounting box|BA11-N]] || none
 
| [[H9273 backplane|H9273]] || Q/CD || 9 || Q18 || [[BA11-N mounting box|BA11-N]] || none
 +
|-
 +
| [[H9274 backplane|H9274]] || Q/Q || 4 || Q18 || [[VT103|VT103]] || none || special connectors for use in the VT103
 
|-
 
|-
 
| H9275 || Q/Q || 9 || Q22 || &nbsp;|| 120 ohms
 
| H9275 || Q/Q || 9 || Q22 || &nbsp;|| 120 ohms
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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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|}
 
|}
  
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'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.
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'Type' indicates whether it is dual-width ('Q') or quad. '# slots' is the number of slots; for Q/Q quad backplanes, the number of dual-width board which can be plugged in is twice this.
  
 
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.
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 +
===MDB backplanes===
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 +
[[MDB Systems]] produced many third-party QBUS options, including backplanes and complete chassis systems:
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 +
{| class="wikitable"
 +
! ID !! Type !! # Slots || 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
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|}
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'Type' indicates slot height and wiring, a value with a slash indicates quad height slots. <!-- if the backplane is quad-height, twice as many dual-height modules will fit. - removed as duplicative of the note under the table above -->
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As with DEC backplanes, MDB backplanes that are Q/Q will damage QBUS cards with CD interconnects.
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==Further reading==
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 +
* ''Micro Backplane Mechanical Mounting Guidelines'', [[MicroNote]] #026
  
 
==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'
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* [http://web.frainresearch.org:8080/projects/pdp-11/micronotes/micronote29.txt Q-bus Expansion Concepts] (uNote #029)
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* [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]

Latest revision as of 18:57, 26 August 2024

QBUS backplanes come mostly 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 backplanes with quad slots are further sub-divided into two types, the so-called Q/Q and Q/CD. In quad Q/Q units, both sides (pairs of 'connectors') of each quad slot are fully wired for QBUS, and so a single slot can hold two separate dual-width QBUS device, memory, etc cards. The device locations are usually arranged for grant priority in so-called 'serpentine' order, i.e. one with the devices in the following 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 QBUS 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 # Slots 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
H9274 Q/Q 4 Q18 VT103 none special connectors for use in the VT103
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. '# slots' is the number of slots; for Q/Q quad backplanes, the number of dual-width board which can be plugged in is twice this.

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 # Slots 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.

As with DEC backplanes, MDB backplanes that are Q/Q will damage QBUS cards with CD interconnects.

Further reading

  • Micro Backplane Mechanical Mounting Guidelines, MicroNote #026

External links

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