Virtual Component and Cluster Test (VCCT) Overview
The Eclipse Board Interconnect Test (BIT) ATPG optionally includes a Virtual Component Cluster Test (VCCT) module, which uses boundary-scan access to detect open and stuck-at faults on the leads of non-scan devices surrounded by boundary-scan devices. VCCT tests an individual non-scan component or a cluster of non-scan components, eliminating the need for physical access to the signal pins of these devices.
How VCCT works
VCCT uses scan cells in boundary-scan devices as virtual ATE channels to drive stimulus into the non-scan logic and detect responses for stuck-at faults. Other test patterns can be supplied to further increase test coverage from an in-circuit test library, design pattern library or may be generated manually. In most instances, Virtual cluster test patterns are generated manually with the help of a logic/fault simulator.
During the test serialization process, VCCT maps the patterns to the scan cells that will serve as inputs and outputs to the device-under-test and orders bit-level data into the correct sequence for the scan path shifting.
Key Capabilities of VCCT
Designating the driver for tristate circuitry
VCCT automatically analyzes and designates a driver when multiple drivers are found on a cluster or component under test.
Scan chain management
VCCT manages the behavior of all the boundary-scan devices in a scan chains during virtual component and cluster testing.
For example, when devices are not directly involved in testing a non-scan device, VCCT automatically places it in EXTEST mode to drive stimulus and capture responses. Scan chain management is fully automated for VCCT testing of individual non-scan devices as well as clusters of non-scan devices.
The most obvious candidates for virtual component testing are non-scan devices surrounded entirely by scan devices. Optionally, BIT's Access Analyzer module generates a Virtual Component Test Report which identifying other devices that can be tested as individual components using VCCT techniques. This report lists additional devices that can be made VCCT-testable, listing the net names and device leads, by placing additional test access points.
Benefits of VCT
- Increases product quality with open and stuck-at fault detection on non-scan devices or clusters
- Eliminates physical access requirements for conventional parts surrounded by boundary-scan logic
- Automatically serializes parallel patterns to test non-scan devices or clusters
- Synchronizes application of serial and parallel test patterns through scan cells and ATE channels