This specification describes circuitry that may be added to an integrated circuit to provide access to on-chip test access ports (TAPs) specified by IEEE Std 1149.1¿¿-2001. The circuitry uses IEEE 1149.1-2001 as its foundation, providing complete backward compatibility, while aggressively adding features to support test and applications debug. It defines six classes of 1149.7 test access ports (TAP.7s), T0-T5, with each class providing incremental capability, building on that of the lower level classes. Class TO provides the behavior specified by 1149.1 from startup when there are multiple on-chip TAPs. Class T1 adds common debug functions and features to minimize power consumption. Class T2 adds operating modes that maximize scan performance. It also provides an optional hot-connection capability to prevent system corruption when a connection is made to a powered system. Class T3 supports operation in either a fourwire series or star scan topology. Class T4 provides for communication with either a two-pin or four-pin interface. The two-pin operation serializes 1149.1 transactions and provides for higher test clock rates. Class T5 adds the ability to perform data transfers concurrent with scan, supports utilization of functions other than scan, and provides control of TAP.7 pins to custom debug technologies in a manner that ensures current and future interoperability.
The standard will define a link between IEEE 1149.1 interfaces in Debug and Test Systems (DTS) and IEEE 1149.1 (JTAG) interfaces in Target Systems (TS). The link defined by this standard introduces an additional layer between these legacy interfaces. This layer may be viewed as an adapter that provides new functionality and features while preserving all elements of the original IEEE 1149.1 (JTAG) interfaces. The standard will define the link behavior (including timing characteristics of signals), protocols, and functionality of the adapters deployed within the DTS and TS. The standard will not modify or createinconsistencies with IEEE 1149.1 (JTAG). The standard will define a superset of the IEEE 1149.1 specification and achieve compliance with IEEE Std 1149.1TM-2001.
The purpose of the standard is to define a debug and test interface that meets an expanding set of challenges facing Debug and Test Systems (many of which have emerged since the inception of the original IEEE Std 1149.1) while preserving the hardware and software investments of the many industries currently using IEEE Std 1149.1-2001.