Stretching the boundary: mixed-signals and P1149.4

Printed circuit boards loaded with both analogue and digital components, especially when chips containing mixed-signal circuits are included, present problems to the test engineer that are becoming increasingly intractable as circuit density and functionality increase. The most urgent of these problems is seen as the ability to perform interconnect testing without the need for physical probing. A structured approach, in which test circuitry is incorporated into the chip in order to provide board-level access to the chip pins, is being developed with a view to establishing a new standard, intended to be compatible with 1149.1. This presentation attempts to describe the present state of this development, and to discuss some of the outstanding issues