If a chain of devices consisted only of boundary scan (JTAG) compliant devices, there would not be too much required testing. However, today’s boards contain complex, non-JTAG devices that interact with the boundary scan devices. Testing just the JTAG devices on the board is always an option. However, developing a test that takes into account the JTAG devices, non-JTAG devices, memory devices, and how these devices interact enhances the overall test, thus achieving higher fault coverage.
In our previous post, we noted that communication between board developers and test developers is key to saving time and money, but more importantly, it is key to developing successful boundary scan applications. Once board and test developers establish a line of communication, test developers can do their part to ensure a successful outcome.
Test developers should know the JTAG and non-JTAG parts on the board under test and what they do or how they may relate to signals from the JTAG parts. For example, to enhance a test to gain better fault coverage, the test developer can match models for non-JTAG devices, transparent devices, and memory devices to circuit locations in the application. Having a boundary scan tool that will account for these conditions in a test will allow test developers to use this information to create one (or all) of the following types of boundary scan tests:
Interconnect tests check the TAP circuits and the connections between boundary scan pins. Paths through resistors, buffers, and logic are part of these tests.
Cluster tests check the connections and interaction between JTAG scan devices and non-scan devices, such as DDR3 and Flash memory. They are also used to program and verify Flash memory.
Custom tests and operations that a user can define. For example, onTAP’s TestGen page provides the tools to customize tests and JTAG scans in an extremely flexible manner.
The more knowledge a test developer has of the board under test, the more quickly the test developer can move through the initial phase of boundary scan test development.
Flynn Systems’ onTAP Boundary Scan Software is a comprehensive tool that facilitates the test development process. Give us a call today at (603)-598-4444 and find out what onTAP can do for you!