Ground Bounce

Ground bounce is an effect on the power rails when many nets are switched in value at the same time. Obviously this is not a normal event; generally a whole set of devices on a single board would not change state all at the same time. However, when implementing the XJTAG Connection Test this is a common event - a large number of nets can be switched to the same value at the same time. This causes sudden drops in the power supply, which can often trigger other events (such as a brown out reset being activated).

To check for this problem, you can limit the number of nets that are changed in any one JTAG cycle, limiting the ground bounce.