As PCB component density has increased, many more new designs are based on boundary scan-enabled parts because physical access has virtually disappeared. Today, complex ICs encompass several forms of built-in test intelligence, and the boundary scan (JTAG) test port has become a popular means of access.
Nevertheless, most engineers and technicians associate boundary scan with PCB troubleshooting, and it is at this level that JTAG Technologies has directed the new JTAG LIVE™ suite of Buzz, Clip, and Script programs. According to Ray Dellecker, the company’s U.S. marketing manager, “JTAG Live is a low-cost, easy-entry tool for anyone who wants to probe a circuit board without having a netlist—you just need the BSDL files. The software can be downloaded from the company’s website and used with a suitable boundary scan controller and interconnecting cables.”
In case you’re wondering, Buzz is named to mimic the buzz of a continuity checker, a good clue to its functionality. A boundary scan controller must be programmed to understand the connectivity among the ICs in the scan chain. Once this has been accomplished, the remaining IC properties are described by the BSDL files. Your controller should be capable of running a simple infrastructure check to ensure that the connectors are plugged in correctly and the scan chain operates.
With Buzz, you can quickly sample, drive, or sense pins from boundary scan devices to check connections between them. As shown in Figure 1, a graphical interface displays the pin-level details.
For many reasons, all the ICs on a PCB generally won’t be boundary scan enabled. This means that there will be areas that Buzz can’t directly reach—that’s inconvenient but not a new boundary scan problem. The solution is to cluster components around boundary scan ICs so you can apply input signals to and sense outputs from the cluster components.
The second module, Clip, is useful in these circumstances. In test engineering jargon, you are creating vector-based cluster test sequences. Each vector in a sequence contains a set of drive values for device inputs and the corresponding sensed values on the device outputs. Clip presents the vectors as a combination of logic analyzer and pattern generator display.
Which brings us to Script, the third module. This level of capability requires some experience to apply in a meaningful way. With Script, you develop test routines based on the open-source Python™ interpreted language, as shown in Figure 2. This means that you can address more complex test applications such as mixed-signal parts, operations that require operator intervention, and looping test patterns to set up device registers. Sample programs are included for RAM testing, flash ID reading, and flash in-system programming.
Three well-organized eight-minute video demos on the company’s website explain enough about each module to get you started. Because the demos work through realistic examples, there’s also sufficient detail to keep you going even if you’re not a boundary scan expert.
Mr. Dellecker emphasized that with JTAG Live, design engineers can use the power of boundary scan to overcome lack of access when they are debugging their hardware. “Until now, prototype debugging with DMMs, analyzers, and scopes has really been hampered by BGAs and other parts with poor or little physical access. JTAG LIVE solves that problem.”
Buzz: Free, Clip: $750, Script: $2,250
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January 2010