An app note from XJTAG about applying test reset to put some devices to JTAG compliant mode. Link here
Some JTAG devices require a specific sequence of states to be applied to some signals in order to put the device into a JTAG-compliant mode. This application note describes how a Test Reset section can be used to describe the required sequence and control its application.
from Dangerous Prototypes http://ift.tt/2trk0ir