Reusable, low-cost, and flexible multidrop system JTAG architecture

A reusable, low-cost, and flexible multidrop system JTAG(1) architecture has been developed at Brocade as an alternative to more expensive commercial solutions. This architecture allows JTAG operations to be driven by a local on-board processor or an external host. An add-drop network design allows all on-board JTAG devices to be grouped into several smaller chains and enables the chains to be combined flexibly for various JTAG operations. By implementing this architecture in a low-cost Complex Programmable Logic Device (CPLD), it has been used in stand-alone single-board systems as well as complex multiboard chassis systems at Brocade.