IEEE 1149.4 2010 Edition, December 9, 2010
A Mixed-Signal Test Bus
This standard defines a mixed-signal test bus architecture that provides the means of control and access to both analog and digital test signals such that the testability structure for digital circuits described in IEEE Std 1149.1-2001 has been extended effectively to provide similar facilities for mixed-signal circuits. In addition to testing of interconnections in the conventional sense of IEEE Std 1149.1-2001, the mixed-signal test bus defined by this standard also provides the means for parametric testing and, optionally, the means to access internal test structures. The standard does not mandate implementation details of the test circuitry, although examples of conformant implementations are given for illustration. Further, the standard develops extensions to Boundary-Scan Description Language (BSDL) as a means of describing key aspects of the implementation of this standard within a particular component. At present, the extensions to BSDL defined by this standard specifically omit the description of any and all analog parameters defined by the standard.
Where structures defined by this standard are incorporated into mixed-signal circuits, the testability problems posed by such circuits are mitigated by way of improving the controllability and observability of mixed-signal designs and supporting mixed-signal built-in test structures in order to reduce both test development time and testing costs and to improve test quality. In particular, these standardized test features allow mixed-signal (analog and/or digital) electronic components, printed circuit assemblies, and electronic systems to be accessible to external or built-in test equipment for interconnect test, parametric test, and internal test. A further purpose of this standard is to define the descriptive elements of BSDL and specified extensions sufficient to support the development of automated test algorithms used for testing interconnections between devices that adhere to this standard and, where practical, between such devices intermixed with devices that incorporate IEEE Std 1149.1-2001 or IEEE Std 1149.6TM-2003 as well. The descriptive elements defined by this standard also largely support the automated construction of analog tests for external components attached to or between components that implement this standard with the caveat that such tests may subsequently require modification to account for undocumented analog features within the conformant components.