An on-chip debug module is a system allowing a developer to monitor and control the execution on a device from an external development platform, usually through a device known as a debugger or debug adapter. With an OCD system, the application can be executed while exact electrical and timing characteristics in the target system (as opposed to a simulator.) The system is able to stop execution conditionally or manually and inspect program flow and memory.
For PIC microcontrollers (MCUs) or dsPIC digital signal controllers (DSC), some device resources may need to be reserved for debug.