Circuitry and method for causing a microcontroller/microprocessor to be on-circuit emulated

摘要

An emulation system for performing an on-circuit emulation operation of a component in a data processing system is described. The component includes a plurality of pins coupled to the remaining circuitry of the data processing system. An emulator is coupled to the remaining circuitry in the same manner as that the component is coupled to the remaining circuitry for issuing an on-circuit emulation control signal to one of the plurality of pins of the component to place the component in an on-circuit emulation mode and for performing the on-circuit emulation operation of the component. A reset circuit is coupled to a reset input of the component and a reset input of the emulator for generating a reset signal to reset the component and the emulator. When the reset signal is in a first voltage state, the component and the emulator are in a reset state. When the reset signal reaches a second voltage state, the component and the emulator exit the reset state. A comparator is coupled to receive the reset signal and a reference voltage for causing the emulator to generate the on-circuit emulation control signal to the one of the plurality of pins of the component when the reset signal is in the first voltage state, and for causing the emulator to maintain the on-circuit emulation control signal applied at the one of the plurality of pins of the component until after both the component and the emulator are out of the reset state such that the component can enter the on-circuit emulation mode and the emulator can start the on-circuit emulation operation after both of the component and the emulator exit the reset state. The voltage level of the reference voltage is higher than the second voltage state of the reset signal. A method of placing the component in the on-circuit emulation mode is also described.