1149.1 scan control transport levels

1149.1 scan constitutes the most general standard of electronic hardware test control available today. Delivery of an 1149.1 scan service from maintenance processors to system components constitutes a universal challenge to systems designers, and a major opportunity for venders in the chip and scan software business. A largely neglected level of scan transport may rapidly become important to system designers. Offerings in the scan distribution arena can be separated into a number of classes, which can be seen to have a certain hierarchy. In the middle of all of these services is a scan control chip. It is driven by a microprocessor and emits a serial scan string. The author describes the four levels of transport