In-circuit emulator (ICE) is one of the oldest embedded debugging tools, and is still unmatched in power and capability.

It is only tool that substitutes its own internal processor for the one in the target system Using one of a number of hardware tricks, the emulator can monitor everything that goes on in this on-board CPU , giving a complete visibility into the target code’s operation.

The emulator is bridge between the target and workstation giving an interactive terminal peering deeply into the target and a rich set of debugging resources. ICE uses another circuit with a card that connect to target processor (circuit) through a socket.

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• An in-circuit emulator (ICE) is a hardware device used to debug the software of an embedded system. It was historically in the form of bond-out processor which has many internal signals brought out for the purpose of debugging. These signals provided information about the state of the processor.

• An in-circuit emulator provides a window into the embedded system. The programmer uses the emulator to load programs into the embedded system, run them, step through them slowly, and view and change data used by the system's software.

• More recently the term also covers JTAG based hardware debuggers which provide equivalent access using on-chip debugging hardware with standard production chips.

• ICE’s attach a terminal or PC to the embedded system. The terminal or PC provides an interactive user interface for the programmer to investigate and control the embedded system.

• In usage, an ICE provides the programmer with execution breakpoints, memory display and monitoring, and input/output control