Properly Managing Common Tri-State Control Cells Boosts Fault Coverage

admin — Wed, 16 Dec 2009 20:16:00 +0000

As the boundary scan community continues looking for new ways to improve test procedures and achieve higher and higher fault coverage, we expect the test tools to compensate for shortcomings in silicon devices or board design. We are constantly exposed to new situations in boundary scan test and new approaches to using boundary scan to achieve better test fault coverage. One item standing in the way of higher, more accurate fault coverage is common tri-state control cells.

Common tri-state control cells are groups of pins on a common net. Just as the name suggests, they are tri-state pins, grouped together by a common function, sharing a boundary scan cell. Though this is efficient for circuitry, it poses some issues during JTAG test. For example, when a single pin on the common cell drives or senses a value, all the pins associated with that cell are forced to perform the same function, simultaneously. This is represented in the following drawing.

Un-handled common tri-state cells can have a negative impact on boundary scan test, dramatically reducing accuracy and fault coverage of opens and shorts tests because multiple pins sharing a common net drive in the same test vector, as displayed in the screen capture below.

In this image, you can see pins U23.AA14 and U36.AE30 are on net U23_AA14. This test is not accounting for the tri-state pins on the common control cell, ultimately compromising fault coverage.

The yellow 0 and 1 characters show drive, or boundary register update, values at each test vector, and the green L and H values show expected boundary register capture values on the vectors following an update.

This image shows the netlist view of the Mv6430 boundary scan device, while the following image displays the pins in an expanded view.

This image shows how the test was revised to account for the tri-state pins on the common control cell. The result is a boost in fault coverage, with the added benefit of making the test more accurate.

As explained in the text box in this screen shot, onTAP accounts for the shared cells and adds additional test vectors to ensure pins do not drive simultaneously, allowing for more comprehensive tests that deliver higher, and most importantly, more accurate, test fault coverage.

Accepting New Turnkey JTAG Projects

admin — Tue, 17 Nov 2009 20:58:35 +0000

Flynn Systems wants to let our users know that we are accepting new JTAG / Boundary Scan projects for Q1-2/10

While our standard Technical Support provides assistance with test and development issues, our boundary scan test development services go beyond onTAP technical support services by taking the boundary scan / JTAG test development and debugging off your plate, allowing you to focus your undivided attention on your core business issues as you move through development and prototyping into manufacturing.

Our Boundary Scan Test Development Service is very popular with both existing and new customers. In fact, 4 out of 5 customers who have used onTAP boundary scan test development services once, immediately recognize the cost and time savings, and return within 4 months with another project. By turning over your JTAG / Boundary Scan test development to Flynn Systems, you are able focus on other aspects of your project without being distracted by developing and debugging boundary scan tests.

We ensure that your boundary scan tests are maximized for the highest possible fault coverage, are completely debugged, and are ready for the manufacturing floor, so the end user only has to “press a button.”

We support our tests and we will support you and/or your contract manufacturer by answering questions and bringing all parties involved up-to-speed with boundary scan test and onTAP procedures and reports.

Our test development features:

JTAG TAP infrastructure tests.
Interconnect tests including detection of opens, shorts, stuck-at, bus-wire, pull-up/down related faults.
Memory tests
Cluster tests of non-JTAG components
Flash programming
In-system programming configuration
Pin-level diagnostics
On-going support

All of our tests are comprehensive, accurate, supported and reliable.

Call us today to get started.

Click here to learn more about onTAP Turnkey Service

Flynn Systems » Boundary Scan JTAG Turnkey Solution

Properly Managing Common Tri-State Control Cells Boosts Fault Coverage

Accepting New Turnkey JTAG Projects