Slide 95 of 173
Notes:
This figure show the basic structure of a boundary-scan cell. One of these cells is added to each I/O port on the chip. One reason that boundary scan may be popular is that the relative cost of adding the scan cells to the I/O pads is low compared to the cost of adding full scan. For example, only a mux is added to the normal I/O path, which does add some delay, but it’s in the context of the already large I/O pad delay. Second, there is some additional logic that has to be added to the Pad buffer, but most of the pad area is dominated by the size of the physical pad, and the additional logic doesn’t increase it by much.
