================================================================================ 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