Data Monitor and Control Interface (DMCI) RTDM Mode
The Real-Time Data Monitor (RTDM) requires a software library to be added to your application code. Applications using the RTDM library communicate with the IDE through a serial port on the microcontroller. This serial interface typically uses interrupts which may affect your application's timing when running in RTDM mode.
The Microchip website currently contains apresentation on the use of the RTDM.

