With IEEE 1687 (aka IJTAG) making its way into a great many chips as a mainstream mechanism for access and control of embedded instrumentation, I’ve taken an interest in explaining this often complicated technology in simple terms. I’ll start with describing the syntax, semantics and overall structure of Instrument Connectivity Language (ICL) and Procedural Description Language (PDL).
The 2013 Revision of the IEEE 1149.1 Standard incorporates support for dynamic data registers that can change in length and organization, unlike those fixed ones specified by the 2001 Revision. This allows, for example, definition of “excludable segments” for the boundary scan register (BSR); perfect for dealing with BSR segments in different power domains, some powered up and some not. How does this work?