IEEE Standard 1149.4 [IEEE99] is titled “Mixed Signal Test Bus” but has become known popularly as “Analog Boundary-Scan”. It is natural to ask, what is “Analog Boundary-Scan”? The digital paradigm we have been using is confusing when we hear the word analog. Could it mean we somehow capture analog voltages and somehow shift them out for viewing (as proposed in [Wagn88])? The answer is “no”. The simplest concept of the 1149.4 Standard is to imagine that we have integrated a portion of an ATE system’s analog measurement bus and multiplexing system into an IC, eliminating the need for bed-of-nails access to it. Since these test resources have been converted from discrete relays, wire wrap and nails into silicon, they will scale with silicon technology as it continues to shrink.
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