Mass interconnect for VXIbus systems - VMEbus Extensions for Instrumentation - Technical

Hewlett-Packard Journal, April, 1992 by Calvin L. Erickson

2. The second step is to determine if a mass interconnect is necessary. The following questions should help in this decision.

How many different DUTs will be tested? More than two or three may indicate a need for mass interconnect. How often will ITAs be changed? More than 400 to 500 times through the life of the system may indicate a need for mass interconnect.

How many lines must be fed through the mass interconnect: more than 200 to 400 general-purpose lines, or more than 20 to 50 coax or power lines? If so, mass interconnect may be appropriate.

What type of signals must be connected? Do appropriate mass interconnect connectors exist? In many cases, a mass interconnect is not appropriate. A high-quality, military-style circular connector may be adequate.

3. The next step is to refine the list made in step 1. Trade-offs must be made between maximizing system flexibility, minimizing complexity and cost, and maintaining critical performance specifications. Particular attention should be given to switching networks. Consider the following:

Custom configurations behind the ICA limit system flexibility, but they also reduce ITA Complexity and cost. Switch networks are essential for minimizing resources and providing system flexibility, but switches have limited life. They add complexity and reduce system performance.

Add lines to the list to account for switching networks, ITA identification, and so on. To each line, attach any important performance specifications such as frequency, voltage, and current.

4. The next step is to make a preliminary layout of the entire system. In most cases, it is best to start with a block diagram. The diagram can then be used to make a sketch of a rack showing all system components. This sketch should include all sources, sensors, switches, mass interconnects, controllers, and so on. Now is the time to think about wiring issues such as grounding and critical lead lengths. Remember to leave room for growth and flexibility.

Selection of the appropriate ICA occurs at this time. This decision should be based on the above considerations and the following:

Is compatibility required with may already exist or they may be planned as part of a large project.

Is compatibility required with an industry standard such as ARINC 608? This would limit the choice to the HP 9420A or the HP E3722A.

What type of signals will be connected? How many lines will be connected? What is the required cycle life of the connectors? The answers to these questions may indicate the use of less-expensive interconnect products such as the HP 34592A quick interconnect.

Is rack space limited? If so, the HP E3720A or HP E3722A may be the best choice. Both ICAs mount on the front of the VXIbus mainframe. Remember, however, that other system components may be reverse mounted behind the HP 9420A without sacrificing rack space. Is a reduction in access to VXIbus front panels acceptable?

Any ICA mounted in front of the VXIbus mainframe will limit access to VXIbus modules. Front-panel indicators will not be visible and modifying modules and wiring will be more difficult.