VXI test instruments and other items are all contained within a VXI module or card.
These modules and cards are contained within a VXI chassis with which they all interface.
In order that VXI instruments, modules or cards from any manufacturer can be used within any chassis, it is necessary that they all conform to tight standards.
VXI module & card types
The VXI standard defines four different sizes of cards or modules that can be used. These are labelled VXI A-size to D size.
- VXI A-size card : This equates to the VME 3U card size. This card size is not widely used, but some basic cards are available.
- VXI B-size card : This equates to the VME 6U size. Like the A-size, this card size is not widely used, but some basic cards are available.
- VXI C-size card : VXI C modules are thicker than VME B-size cards to provide space for improved EMI shielding, as well as to allow for better airflow for cooling. This is the most popular size for VXI cards. It enables systems to be smaller than if they used D sized cards, but allows for significant levels of functionality.
- VXI D-size card : The VXI D-size card is different from the others in that it has a third connector, P3, which is uniquely defined for VXI applications. Although D sized cards allow significant advantages in terms of board space, these cards are really only used for very complex instruments in large functional testers.
|VXI Card / Module Sizes & Spacing|
|Card Designation||Size (mm)||Spacing (mm)||Connectors|
|Size A||100 x 160||20||P1|
|Size B||233 x 160||30||P1, P2|
|Size C||233 x 34||30||P1, P2|
|Size D||367 x 340||30||P1, P2, P3|
VXI device types
There are two formats for a VXI controller to communicate with the devices within a system.
- Register-Based Devices:All VXI modules contain configuration registers that can be accessed by the controller. Information including VXI device, its type, model and manufacturer, address space, and memory requirements can all be accessed. This is a basic level of communication with devices, and those which only this minimum level of capability are called VXI Register-Based devices.
Using a common set of configuration registers, a software module termed the centralized Resource Manager is able to undertake automatic system and memory configuration when the system is first initialized.
- Message-Based Communication:A second, and more sophisticated devices are defined by VXI. Termed Message-Based devices, they possess communication registers and configuration registers which can communicate at a basic level using the VXI-specified Word Serial Protocol. It may then be possible for, higher-performance communication channels, such as shared-memory channels, to be established to take advantage of the VXIbus bandwidth capabilities.