================================================================================
Note 35.0                Backplane Expansion/Termination              No replies
FURILO::GIORGETTI                                   469 lines   3-SEP-1985 17:22
--------------------------------------------------------------------------------


      +---------------+                                    +-----------------+
      | 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
Page 2 of 8


           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
                                                           Page 3 of 8


      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.





                                  329

uNOTE # 035
Page 4 of 8


           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
                                                           Page 5 of 8



      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

                                  331

uNOTE # 035
Page 6 of 8


      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
                                                           Page 7 of 8


               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

uNOTE # 035
Page 8 of 8


                                            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

