IEEE 1149.6: Testing Advanced I/O

IEEE Standard 1149.6 [IEEE03] addresses “Boundary-Scan Testing of Advanced Digital Networks” but has become known popularly as “The AC EXTEST” standard. This popular title is really a misnomer. The formal title speaks of testing of advanced digital networks, meaning the I/O structures between ICs. During the development of IEEE Standard 1149.1 over a decade ago, communication between ICs was conducted over single wires. Now we see a growing trend for differential transmission of signals, using two wires per signal channel, and we also are beginning to see AC coupling structures between ICs. AC-coupled differential channels are a signaling process that effectively defeats the testing capabilities of IEEE 1149.1.