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

In an emulation system having an emulation means for performing an on-circuit emulation operation of a component of a data processing system, wherein the component includes a plurality of pins coupled to the remaining circuitry of the data processing system, wherein the emulation means is coupled to the remaining circuitry in the same manner as that the component is coupled to the remaining circuitry, wherein the plurality pins of the component are electrically disconnected with the remaining circuitry when the component is placed in an on-circuit emulation mode during the on-circuit emulation operation, a control circuitry for placing the component in the on-circuit emulation mode, comprising:

• (A) reset means coupled to a reset input of the component and a reset input of the emulation means for generating a reset signal to reset the component and the emulation means, wherein when the reset signal is in a first voltage state, the component and the emulation means are in a reset state, wherein when the reset signal reaches a second voltage state, the component and the emulation means exit the reset state;
• and
• (B) comparator means coupled to receive the reset signal and a reference voltage for causing the emulation means to generate an on-circuit emulation control signal to one of the plurality of pins of the component to place the component in the on-circuit emulation mode when the reset signal is in the first voltage state, and for causing the emulation means to maintain the on-circuit emulation control signal applied at the one of the plurality of the component until after both the component and the emulation means are out of the reset state such that the component can enter the on-circuit emulation mode and the emulation means can start the on-circuit emulation operation after both of the component and the emulation means exit the reset state, wherein the voltage level of the reference voltage is higher than the second voltage state of the reset signal.

A method of placing a component of a data processing system in an on-circuit emulation mode for an on-circuit emulation operation, wherein the component includes a plurality of pins coupled to the remaining circuitry of the data processing system, wherein the method comprises the steps of:

• (a) coupling an emulation means to the remaining circuitry of the data processing system in the same manner as that the component is coupled to the remaining circuitry;
• (b) generating a reset signal to a reset input of the component and a reset input of the emulation means, wherein when the reset signal is in a first voltage state, the component and the emulation means are in a reset state, wherein when the reset signal reaches a second voltage state, the component and the emulation means exit the reset state;
• (c) causing the emulation means to generate the on-circuit emulation control signal to one of the plurality pins of the component when the reset signal is in the first voltage state, and causing the emulation means 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 emulation means are out of the reset state such that the component can enter the on-circuit emulation mode and the emulation means can start the on-circuit emulation operation after both of the component and the emulation means exit the reset state, wherein the component does not include a dedicated on-circuit emulation mode enable input, wherein the emulation means performs the on-circuit emulation operation on the component when the component is in the on-circuit emulation mode.