IEEE P1149.4-almost a standard

The IEEE P1149.4 Mixed-Signal Test Bus Working Group is on the cusp of delivering a document that will finally standardize the architecture for, and the method of access to, the analog portion of mixed-signal circuits for test and diagnostic applications. This Standard will have the same profound effect on the design and test community that IEEE 1149.1 had previously. P1149.4 gives the test infrastructure the capability to measure discrete impedances external to devices supporting the Standard using a 6-wire bus. This bus uses 4 of the same signals used today to support 1149.1 compliant devices and subsystems. This paper will detail the basic architecture; give some design-specific information and data learned through the Standard's development process; relate results from several test devices; and provide a basic example of usage.