Method and apparatus for processor emulation

A data processing apparatus, comprising:

• data processing circuitry for performing data processing operations on data;
• an input/output bus which is coupled to and normally controlled by said data processing circuitry and is connectable to a peripheral circuit for permitting communication between said data processing circuitry and said peripheral circuit;
• and
• emulation circuitry coupled to said input/output bus for selectively taking control of said input/output bus in substitution for said data processing circuitry and emulating on said input/output bus operations normally performed on said input/output bus by said data processing circuitry when said data processing circuitry controls said input/output bus, said emulation circuitry including serial scanning circuitry for providing to and receiving from said input/output bus signals which are normally provided to and received from said input/output bus by said data processing circuitry when said data processing circuitry controls said input/output bus, said serial scanning circuitry being connectable to an emulation controller for permitting serial data transfer between the emulation controller and said data processing apparatus, and said emulation circuitry including control circuitry connected to said serial scanning circuitry and connectable to the emulation controller for, when connected to the emulation controller, permitting said serial scanning circuitry to provide and receive said signals while serial data is being transferred in a continuous serial data stream between the emulation controller and said serial scanning circuitry.

A data processing system, comprising:

• a data processing apparatus including data processing circuitry for performing data processing operations on data, and an input/output bus coupled to and normally controlled by said data processing circuitry for transferring information into and out of said data processing apparatus;
• a peripheral circuit connected to said input/output bus for communication with said data processing apparatus;
• and
• said data processing apparatus including additional circuitry coupled to said input/output bus for selectively taking control of said input/output bus in substitution for said data processing circuitry and performing one of (1) a test operation wherein said peripheral circuit is tested using said input/output bus and said additional circuitry and (2) an emulation operation wherein said additional circuitry emulates on said input/output bus operations normally performed on said input/output bus by said data processing circuitry when said data processing circuitry controls said input/output bus, said additional circuitry including serial scanning circuitry coupled to said input/output bus for supporting one of said test operation and said emulation operation, said serial scanning circuitry being connectable to an external controller for permitting serial data transfer between the external controller and said data processing system, and said additional circuitry including control circuitry connected to said serial scanning circuitry and connectable to the external controller for, when connected to the external controller, permitting one of test signals for testing said peripheral circuit and emulation signals for emulating operations of said data processing circuitry to be transferred between said serial scanning circuitry and said input/output bus while serial data is being transferred in a continuous serial data stream between the external controller and said serial scanning circuitry.