| 摘要 |
An emulation device which enables a functional circuit to support self emulation. A serial scan testability interface has at least first, second and third scan paths, said first scan path being provided for applying digital information to the functional circuit for use in emulation of the functional circuit. A first state machine connected to said second scan path has a first state selected from among a first set of states. A second state machine connected to said third scan path has a second state selected from among a second set of states. The emulation device performs an emulation command based on a combined first state of said first state machine and second state of said second state machine. The state of the first state machine indicates a primary portion of the emulation command denoting an emulation command class. The state of the second state machine indicates a secondary portion of the emulation command consisting of a subtype within the emulation command class. Both state machines return to a default "no-op" state following performance of an emulation command prior to accepting new data. The first scan path is used for JTAG when the first state machine is the default "no-op" state. Alternatively, the first scan path is used for JTAG when the first state machine is a "normal JTAG operation" command class. An unused JTAG command indicates to the first state machine that the following bit string is a command class and not a JTAG operation.
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