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Note 35.0 Backplane Expansion/Termination No replies
FURILO::GIORGETTI 469 lines 3-SEP-1985 17:22
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+---------------+ +-----------------+
| d i g i t a l | | uNOTE # 035 |
+---------------+ +-----------------+
+----------------------------------------------------+-----------------+
| Title: Backplane Expansion/Termination | Date: 19-Jul-85 |
+----------------------------------------------------+-----------------+
| Originator: Jack Toto | Page 1 of 8 |
+----------------------------------------------------+-----------------+
The following MicroNote discusses the termination and expansion
configurations which are SUPPORTED by Digital Equipment Corporation.
These configurations will deal with 18 and 22-bit Q-bus processors,
backplanes and enclosures. Not all cases presented in this MicroNote
meet FCC regulations, and only those that do are so marked.
The MicroNote is partitioned as follows:
1. System configurations
2. Single Box expansion/termination rules.
3. Multiple box expansion/termination rules.
4. Configuration/case reference chart.
5. Supported single box configuration cases.
6. Supported multiple box configuration cases.
1. SYSTEM CONFIGURATION
--------------------
The following is a list of single and multiple backplane termination
rules which must be followed when termination is required. Further
explanation of these rules can be found in MicroNote # 029, the
Microcomputers Products Handbook (EB-26078-41), the Microcomputer
Products Configuration Guide (EB-27318-68), and generally the user guide
for any of the CPUs.
The LSI-11 Bus system can be divided into two types:
1. Systems containing one backplane.
2. Systems containing multiple backplanes
Before configuring any system, module/system characteristics must be
known. These characteristics are:
1. Power consumption. The +5 Vdc and +12 Vdc current
requirements.
2. AC bus loading. The amount of capacitance that a module
presents to a bus signal line. AC loading is expressed in
terms of ac loads where one ac load equals 9.35 pf of
capacitance.
327
uNOTE # 035
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3. DC bus loading. The amount of dc leakage current a module
presents to a bus signal when the line is high (undriven). DC
loading is expressed in terms of dc loads where one dc load
equals 210 ma nominal.
4. Total backplane loading must include ac and dc loads and the
power consumption of the processor, modules, terminator module,
and backplane.
5. Processor termination, class as either 120 ohms or 240 ohms, as
follows:
OPTION TERMINATION MODEL NAME
------------------------------------------
A. KDF11-A 240 OHMS LSI 11/23
B. KDF11-B 120 OHMS LSI 11/23 +
C. KDJ11-A 240 OHMS LSI 11/73
D. KDJ11-B 120 OHMS PDP 11/73
E. MicroVAX I 120 OHMS MicroVax I CPU
F. MicroVax II 240 OHMS MicroVax II CPU
Power consumption, ac loading, and dc loading specifications for each
module can be found in sources mentioned earlier.
2. SINGLE BACKPLANE TERMINATION RULES
----------------------------------
1. When using a processor with 240 ohms termination, the bus can
accommodate up to 20 ac loads (total) before additional
termination is required. If more than 20 ac loads are
included, the far end of the bus must be terminated with 120
ohms, although termination of 240 ohms is optimum. Following
the addition of at least the minimum termination up to 35 ac
loads may be present in a single backplane.
2. When using a processor with 120 ohms termination, up to 35 ac
loads (total) may be present before additional termination is
required. If more than 35 ac loads are included, the far end
of the bus must be terminated with 120 ohms. When this has
been done up to 45 ac loads may be present.
3. The bus can accommodate up to 20 (total) dc loads. This is
true in all cases.
4. The bus signal lines on the backplane can be up to 35.6 cm (14
in) long.
328
uNOTE # 035
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3. MULTIPLE BACKPLANE TERMINATION RULES
------------------------------------
1. Up to three backplanes maximum can be configured in a multiple
backplane system.
2. The signal lines on each backplane can be up to 25.4 cm (10 in)
in length.
3. Terminated multiple backplane systems can accommodate up to 44
ac loads, for two backplane systems, and 66 ac loads for three
backplane systems. In multiple backplane systems no more than
22 ac loads may be present in any one backplane, nor may any
unused ac loads from one backplane be added to the next
backplane. It is best to load each backplane equally, but if
not possible, then the first and second backplanes should have
the highest number of ac loads.
4. DC loading for all modules in all backplanes cannot exceed 20
loads (total).
5. Both ends of the bus must be terminated with 120 ohms. This
means that the first and last backplanes must have an impedance
of 120 ohms. To achieve this, each backplane must be lumped
together as a single point. The resistive termination may be
provided by combining two of the modules in the backplane; the
processor providing 240 ohms to ground in parallel with an
expansion module providing 240 ohms to give the needed 120 ohms
termination. Alternately a processor with 120 ohms termination
would require no additional termination on the expansion module
to provide 120 ohms in the first box. The 120 ohms termination
in the last box may be provided in three ways. The termination
resistors may reside either on the bus expansion module, or on
a bus terminator module such as a BDV11, or on the backplane
itself as in the case of the H9275 and BA23-A backplanes.
6. The cable lengths connecting the first and second backplane are
61 cm (2 ft) or greater.
7. The cables connecting the second and third backplane are 122 cm
(4 ft) longer or shorter than the cables connecting the first
and second backplanes.
NOTE
NEITHER THE FIRST OR SECOND BOX CABLE MAY BE
SHORTER THAN 2 FEET IN LENGTH AND BOTH CABLES
MUST DIFFER IN LENGTH BY 4 FEET.
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uNOTE # 035
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8. The combined length of the cables can not exceed 4.88 m or 16
feet.
9. The cables must have a characteristic impedance of 120 ohms.
4. CONFIGURATION/CASE REFERENCE CHART
----------------------------------
The chart below is designed to be a quick reference to a specific
configuration combination of CPU and system box(es). The actual cases
themselves are listed after the chart.
To use the chart below, find the CPU that is in the system and the
number of backplanes or enclosures that you will be using. The
intersection of the two parameters will give you the case/variation
number that is valid for that configuration. The case/variation will be
listed as a case number followed by the variation number listed as ".n"
(where n is an integer from 1 to 9). Ex. case 1.2 represents case 1,
with variation 2.
SYSTEM CONFIGURATION CHART
+----------------------+--------------+---------------+---------------+
| PROCESSOR | SINGLE BOX | TWO BOX | THREE BOX |
+----------------------+--------------+---------------+---------------+
| KDF11-A 240 OHMS | CASE 1 | CASE 4.1 | 18-BIT SYSTEMS|
| | CASE 2 | CASE 4.2 | ONLY |
| | | CASE 4.3 | |
+----------------------+--------------+---------------+---------------+
| KDF11-B 120 OHMS | CASE 1 | CASE 3.1 | 18-BIT SYSTEMS|
| | CASE 2 | CASE 3.2 | ONLY |
| | | CASE 3.3 | |
| | | CASE 3.4 | |
+----------------------+--------------+---------------+---------------+
| KDJ11-A 240 OHMS | CASE 1 | CASE 4.1 | 18-BIT SYSTEMS|
| | CASE 2 | CASE 4.2 | ONLY |
| | | CASE 4.3 | |
+----------------------+--------------+---------------+---------------+
| KDJ11-B 120 OHMS | CASE 1 | CASE 3.1 | 18-BIT SYSTEMS|
| | CASE 2 | CASE 3.2 | ONLY |
| | | CASE 3.3 | |
| | | CASE 3.4 | |
+----------------------+--------------+---------------+---------------+
| MICROVAX I 120 OHMS | CASE 2 | CASE 3.1 | NOT |
| | | CASE 3.2 | APPLICABLE |
| | | CASE 3.3 | |
| | | CASE 3.4 | |
+----------------------+--------------+---------------+---------------+
| MICROVAX II 240 OHMS | CASE 2 | CASE 4.1 | NOT |
| | | CASE 4.2 | APPLICABLE |
| | | CASE 4.3 | |
+----------------------+--------------+---------------+---------------+
330
uNOTE # 035
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5. SINGLE BOX SYSTEMS CONFIGURATION CASES
--------------------------------------
Single box 18 or 22 bit system configurations can be terminated the
following two ways. The two configuration cases presented in this
section will give optimum bus termination to 120 ohm processor based
systems and acceptable termination to 240 ohm processor based systems.
CASE 1. Use an unterminated enclosure/backplane with a termination
card such as the BDV11 in the first unused slot. This card should
be ECO'd to etch revision E, when used in 22-bit systems . This
card should also have the on board processor and memory diagnostics
disabled if it is going to be used to terminate a system with the
KDJ11-A or KDJ11-B as the CPU. (refer to MicroNote # 003) The
following enclosures and backplanes are unterminated;
OPTION SYSTEM SIZE
-----------------------
A. BA11-SA 18/22 BIT
B. BA11-M 18 BIT
C. BA11-N 18 BIT
D. H9270-Q 18/22 BIT
E. H9281-QA 18/22 BIT
F. H9273-A 18 BIT
CASE 2. Use an enclosure/backplane which is already terminated.
All but one of Digital's backplanes are terminated with 120 ohms,
and will meet the minimum termination required for additional ac
loading beyond the capabilities of an unterminated backplane. The
one backplane that is not terminated at 120 ohms is the one found
inside of the BA23-A enclosure. This option is terminated at 240
ohms. This enclosure is the only option that will provide optimum
termination for 240 ohm CPUs. The following table list all of the
terminated enclosures and backplanes available from Digital
Equipment Corporation:
OPTION SYSTEM SIZE TERMINATION
-------------------------------------------------
A. BA23-A 18/22 bit 240 OHMS
B. H9275-A 22 BIT (not expandable) 120 OHMS
C. H9281-QB 18/22 BIT 120 OHMS
D. H9281-QC 18/22 BIT 120 OHMS
6. MULTIPLE BOX SYSTEMS CONFIGURATION CASES
----------------------------------------
Multiple box configurations can be up to three boxes maximum. However
currently only 18-bit three box systems can be configured and terminated
properly. Therefore cases 3 and 4 described below will deal only with
two box 22-bit system configurations using CPUs of either impedance as
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18-bit systems are sufficiently documented as noted below.
NOTE
FOR 18-BIT MULTIPLE BOX SYSTEMS USING A CPU CONTAINING
EITHER 120 OR 240 OHMS OF IMPEDANCE THE PROCEDURE FOR
EXPANDING FROM A ONE BOX SYSTEM TO A TWO BOX SYSTEM IS
DOCUMENTED IN SEVERAL TECHNICAL RESOURCES, SUCH AS THE
EXPANSION PRODUCTS HANDBOOK (EB24836-75/68) AND THE
BA11-N TECHNICAL MANUAL (EK-BA11N-TM-001). A
PARTICULARLY GOOD RESOURCE FOR 18-BIT MULTIPLE BACKPLANE
EXPANSION AND TERMINATION GUIDELINES IS THE LSI SYSTEM
SERVICES MANUAL (EK-LSIFS-SV-005).
CASE 3. This case deals with a 120 ohm CPU. The 120 ohms of
impedance on the CPU does not have to matched in the first box, but
does have to be matched at the far end of the bus which will be
located in the second box. This will generate four variations to
the case dealing with 120 ohm CPUs. All four of these variations
will have in common the BCV2A expansion assembly. This option
contains two paddle cards (M9404-00 at 0 ohms and the M9405-YA at
120 ohms) and the BC02D-03 interconnect cable. The card for
expanding the bus out of the first box (M9404) will be installed in
the first unused slot of the first backplane, with the cable
connected to it the bus will be carried to the second backplane.
Here the bus is terminated by installing the termination card
(M9405) in the first slot of the second backplane.
VARIATION 1: Use two unterminated enclosures such as the
BA11-SA master box and the BA11-SE expansion box, connected
with the BCV2A. This configuration is not FCC compliant and
places the task of FCC compliance on the user. FCC compliance
can be obtained by rack mounting these two enclosures in an
H9642 cabinet and using the H349 distribution panel to make
connections from the system to the outside environment, using
the appropriate option cabinet kits. This cabinet system has
been tested by Digital Equipment Corporation for FCC
compliance.
NOTE
THE NEXT TWO VARIATIONS CAN BE MADE FCC
COMPLIANT BY RACK MOUNTING BOTH BOXES IN AN
H9642 CABINET THAT HAS THE H9544-AJ SIDE
PANELS. THESE SIDE PANELS ALLOW FOR THE SIDE
TO SIDE AIR FLOW FOR THE BA23 ENCLOSURE. ALSO
INCLUDED IN THIS CABINET CONFIGURATION IS THE
H3490 PATCH PANEL WHICH IS USED FOR MAKING
CONNECTIONS FROM THE SYSTEM TO THE OUTSIDE
ENVIRONMENT VIA THE APPROPRIATE OPTION MODULE
CABINET KITS. (REFER TO THE MICROCOMPONETS
CONFIGURATION GUIDE FOR DETAILS)
332
uNOTE # 035
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VARIATION 2: Use the BA23 enclosure as the primary enclosure
and the BA11-SE as the expansion chassis, again using the BCV2A
as the interconnect for the two enclosures. The termination
that exist on the BA23 backplane must be removed because the
that the CPU has 120 ohms of impedance in the first box and
does not require any additional termination at this point.
VARIATION 3: Use two BA23 enclosures. When using two BA23-A
enclosures and the BCV2A expansion assembly option the
termination from both backplanes must be removed. This is due
to the fact that the 120 ohms of CPU impedance does not have to
matched in the first backplane of a multiple backplane system
and that the BCV2A will put the required termination into the
last backplane of this configuration. The interconnect for the
two boxes will again be the BCV2A.
VARIATION 4: A final variation to the 120 ohm CPU system would
be to follow the same scenario as in the first three
variations, but using a mix of some terminated and unterminated
backplanes as opposed to system enclosures. These backplanes
and their termination states are listed in cases one and two.
CASE 4. This case deals with the 240 ohm CPUs. As stated in the
termination rules for 240 ohms CPUs, the processors impedance
should be matched in the first box. This would bring the total
impedance in the first box to 120 ohms which is the ideal
impedance. This 120 ohms from the first box, would be matched at
the far end of the bus which will be located in the second box.
Configurations with 240 ohm CPUs have three variations. All of the
case 4 variations will have in common the BCV2A expansion assembly.
The installation of this option is explained above, in the section
introducing two box systems.
VARIATION 1: This case variation uses the BA23 enclosure as
the primary box and expands into a BA11-SE. Using this
configuration requires that the termination on the backplane of
the BA23 be left in. This will provide for an optimum
impedance match in the first box. The bus will be terminated
at the far end in the second box via the expansion assembly
termination card (M9405-YA). This configuration as is will not
be FCC compliant however following the guide lines from the
CASE 3 variations FCC compliance can be achieved.
VARIATION 2: The two enclosures used here will be the BA23
system box and the BA23 expansion box. While this
configuration resembles case 4 with variation 1, the only
change will be the removal of any termination from the second
(expansion) backplane. Interconnect between the two boxes and
FCC compliance can be achieved as described.
333
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NOTE
WHEN CONFIGURING MULTIPLE BACKPLANE SYSTEMS
USING THE BA23-A BOX WITH THE RQDX1 RD/RX
CONTROLLER INSTALLED, CONSIDERATION SHOULD BE
GIVEN TO THE PLACEMENT OF THE CONTROLLER AND
ITS RELATIONSHIP TO THE DEVICES THEMSELVES.
FURTHER WHEN USING MULTIPLE BA23-A ENCLOSURES
IT BECOMES POSSIBLE TO HAVE THE BEVNT LINE FROM
BOTH OF THE POWER SUPPLIES TO BE ACTIVE AT THE
SAME TIME. THERE SHOULD ALWAYS BE ONLY ONE
BEVNT LINE ACTIVE AT ANYTIME, THEREFORE CARE
MUST TAKEN TO AVOID THIS CONFLICT.
VARIATION 3: This final case 4 variation deals with the use of
terminated and unterminated backplanes rather than enclosures.
Using a mix of these products the configurations would resemble
the first two for case 4, and would follow the same rules for
proper termination.
334