Abstract: Test apparatus (10) performs non-destructive testing of an object (O) to determine if it has flaws or defects. An ultrasonic wave (W) is generated and directed at the object. A return wave (R) reflected by the object is received and analyzed to determine if a flaw or defect. The return wave is converted to digital data which is stored for purposes of later analysis. For this purpose, digital signals containing the data are routed over a quiet bus (24). Digital signals are routed over the bus prior to generation of an ultrasonic wave to establish test parameters. Digital noise may occur during the transmission. A controller (22) controls routing of digital signals over the bus. The controller inhibits the flow of digital signals over the bus during that portion of an operational cycle of the apparatus during which the ultrasonic waves are produced and return waves evaluated. The controller allows transmission of digital signals over the bus at other times.