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

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

The HP 75000 family of VXIbus products includes a set of interconnect hardware that enables automatic test system developers to mount DUTs easily to HP's VXIbus mainframe.

The interconnect hardware in an automatic test system consists of the components that connect the device under test (DUT) to the test system mainframe. Typically, automatic test equipment (ATE) product development has focused on instrumentation, controllers, and software. The result is that the interconnect hardware in a test system has become a major component of system cost. In most test systems, interconnects consist of discrete wire and connector harnesses, and their fabrication is custom and labor intensive. Many systems also require a mass interconnect for interfacing with multiple devices under test DUTs.

The development of the VXIbus has brought these issues into sharper focus. Greater density requires that more signal lines must be packed into less space. Higher speeds require shorter lead lengths and better connectors. Finally, economics and time-to-market constraints demand standard parts suitable for many applications. This paper discusses the development of mass interconnect products specifically for VXIbus systems. Based on the HP ATS 2000 system resource interface, these products mount directly on the front of the HP VXIbus mainframe. This paper also discusses the trade-offs involved in incorporating a mass interconnect into a VXIbus test system.

HP Interconnect Components

As part of the HP 75000 family of VXIbus instruments, a number of mass interconnect products are available for use in VXIbus test systems. These products, known as the HP 75000 system resource interface, allow a single test system to service a large variety of units under test. Mg. 1 shows the products included in the HP 75000 system resource interface.

The interface connector assembly (ICA) is the heart of the system. It serves as the primary interface between the test system and the DUT. The ICA is typically rackmounted and wired directly to test system resources such as switching, sensors, and sources. The ICA provides locations for mounting ICA connector blocks and aligning connector blocks and their mating halves, and a mechanism for overcoming the connector mating forces. The HP 75000 system resource interface connector assemblies include:

The HP 9420A ICA. This is the standard rack-mount version shown in Fig. 1.

The HP E3720A VXIbus ICA. This ICA mounts directly on the front of a VXIbus mainframe. It also allows direct access to VXIbus modules and provides the greatest opportunity for short lead length.

The HP E3722A hinged ICA. This ICA also mounts directly on the front of a mainframe and hinges down to allow access to VX[bus modules.

The interface test adapter (ITA) is the frame that mates with the ICA. It provides locations for mounting connector blocks. Typically, several ITAs are purchased, one for each type of DUT. A frame or fixture is often built on the ITA, customizing it to the particular DUT. Mg. 2 shows an ITA customized for functional testing of a printed circuit board. The HP 75000 system resource interface includes two different ITAS:

The HP 9421A. This ITA is used with the HP 9420A ICA and the HP E3722A hinged ICA.

The HP E3721A VXIbus ITA. This ITA is used with the HP E3720A VXIbus ICA.

Different kinds of connector blocks are available for use with the ICAs and ITAs (see Mg. 3). These blocks are wired and then installed in the appropriate location within the ICA or ITA. The three primary choices are 192-pin general-purpose, 36-contact coaxial, and 24-contact power. These connector blocks are compatible with each ICA and ITA choice listed above.

Customer Requirements

The list of customer requirements for mass interconnect in a VXIbus test system is extensive. Most of these requirements derive from the need to test a large variety of DUTS. The mass interconnect must have a variety of connectors that can handle different types of signals. These include low-level precision signals, high-frequency signals, and high-power signals. Sometimes, it is necessary to keep lead lengths as short as possible to maintain signal integrity. The connectors must have a long life to allow frequent changes of the ITA. The ITA must have a rugged and versatile construction to allow the addition of a variety of fixtures suitable for testing everything from printed circuit assemblies to automobiles. Most test systems require many modes of wire routing. For the VXIbus, these modes include: VXI-to-ICA. For example, a VXIbus relay module can have many connections directly to an ICA connector block. VXI-to-VXI. The same relay module can have an analog bus connection to a neighboring module in the same mainframe.

VXI-to-System. A VXIbus slot 0 module may require an

HP-IB connection to the controller.

ICA-to-System. A non-VXIbus signal generator may require connection to an ICA connector block.

Test systems must be easy to configure and reconfigure. This requires that VXIbus modules must be easy to install and remove. Wiring should be accessible. Standard cable assemblies should be available that satisfy most of the wiring requirements. Different ICA configurations should be available for mounting in front of VXIbus or standard rack mounting.