An adaptation of standard boundary cell architecture defined by the IEEE 1149.1 Joint Test Action Group (JTAG) interface standard to provide paths to functional circuitry via the re-use of JTAG standard test data registers (TDR) and interface. Existing multi-core processor solutions are covered, but an expansion for a more generic solution is provided. In general, an integrated circuit is provided with a plurality of function registers along with a plurality of I/O units. The I/O units are arranged in a serial communications chain located around the boundary of the integrated circuit's functional circuitry. Each of the I/O units include JTAG standard serial TDR in serial communication with adjacent I/O units. Moreover, each I/O unit includes JTAG standard parallel TDR that is associated with and in parallel communication with the I/O unit's JTAG standard serial TDR. Further still, a digital logic interface is configured to control the direct transfer of data between the JTAG standard parallel TDR and a corresponding one of the plurality of function registers. As a result of the re-use of existing boundary scan architecture, a significant reduction in wiring congestion is realized. Thus, asynchronous communication is provided without sacrificing valuable integrated circuit real estate.