Software interface enables early detection and repair of PCB errors

Developed by boundary-scan hardware and software tool supplier XJTAG, XJTAG DFT Assistant allows users to detect and correct JTAG errors at the design stage before the PCB is produced, preventing costly re-spins and project delays.

“PCBs have become increasingly densely populated, and accessing pins under packages such as Ball Grid Arrays (BGAs) has been virtually impossible,” said Kishore Karnane, Product Management Director, PCB Group, Cadence. “Boundary scan addresses this problem by providing electrical access to compliant integrated components on a PCB using a JTAG chain, but it is also imperative that any errors in the JTAG chain are corrected early. XJTAG DFT Assistant allows engineers to determine whether JTAG chains are correctly connected and terminated during schematic capture, early in the design process.”

XJTAG DFT Assistant is composed of two key elements: XJTAG Chain Checker and XJTAG Access Viewer. XJTAG Chain Checker identifies common errors in a JTAG scan chain, such as incorrectly connected and terminated Test Access Ports (TAPs), and reports them to the developer. Otherwise, a single connection error would inhibit the entire scan chain from working. XJTAG Access Viewer overlays the extent of boundary scan access onto the schematic diagram, allowing users to instantly see which components are accessible using boundary scan, and where test coverage can be further extended. Engineers can highlight the nets individually to show read, write, power/ground and the nets without any JTAG access on the schematic.

“We need to determine early in the design phase how to maximise test coverage using the minimum number of test points, so it is vital to know what JTAG access is available at the schematic stage,” said Urs Allemann, Director of design services at ed electronic design. “The XJTAG DFT Assistant for OrCAD Capture makes it easy for us to see the test coverage as the design evolves. This allows us to optimise our testing before the PCB is produced.”

While the first prototype is being manufactured, XJTAG DFT Assistant allows engineers to export a preliminary XJTAG project from OrCAD Capture to the XJTAG development software, where additional tests can be developed. Hardware can then be tested as soon as it is available.

XJTAG DFT Assistant software is now included with OrCAD Capture 17.2-2016 QIR 2 at no additional cost; users of version 17.2 or higher can download the software here.