The SW Engineer has some other requirements when working over JTAG. He hopefully has a stable hardware platform, and his projects tend to get larger and larger. For him the JTAG Debugger needs to be fast, reliable and very flexible to adapt to various Operating system environments. Most OS Vendors have seen the requirements and are offering solutions, which are tightly integrated into their Programmers IDE. As these people usually see only their requirements, it makes a lot of sense to be able to isolate the CPU in the JTAG chain, or have the CPU be the first in the Scan chain. Most of these SW tools cannot tolerate other devices in the scan chain and simple do not work in such an environment. A simple jumper on the target board, which isolates the connection to the other devices in the JTAG chain, can make live much easier for the software guys. The most useful tools here run over Ethernet, as this allows standard APIs to be used with the target resources.