PXI extends reach of boundary scan

摘要

Boundary-scan technology arose to simplify the testing of connections on fine-pitch printed-circuit boards. Now, as test-equipment manufacturers combine the features of PXI-based instruments with boundary scan, faster testing and new test options are becoming available. Boundary scan was developed in the late 1980s by the Joint Test Action Group (JTAG) and was approved as IEEE 1149.1 in 1990. The basic principle (Figure 1) is that boundary-scan-compliant devices incorporate a scan register at each digital I/O pin, connected together in a chain. Each register provides an input cell that can measure the signal present on the pin, an output cell that can send a signal to the pin, and storage cells that connect to form a shift register. Connecting boundary-scan devices together extends the shift register, creating a single chain that allows access to every digital I/O pin on a circuit board.