Interface system between mixed-signal electronic components, assemblies, and systems, and external or built-in-test equipment to provide those components, assemblies, and systems with testability attributes.
IEEE 1149.4-1999 history
2010IEEE 1149.4-2010 A Mixed-Signal Test Bus (IEEE Computer Society)
1999IEEE 1149.4-1999 Standard for a Mixed Signal Test Bus IEEE Computer Society Documents