1. An in-system debug (ISD) apparatus for debugging a program residing in a microcontroller of a microcontroller system, the apparatus comprising: a system board of the microcontroller system; a microcontroller having built-in ISI) hardware circuitry mounted on the system board having a pin that provides a first function during a normal mode of operation and a second data relay function during an internally controlled in-system debugging mode of operation for relaying data generated by the microcontroller responsive to executing the program to an external monitoring system without affecting the normal I/O operations of the microcontroller, and the external monitoring system, comprising: an ISD interface board coupled to the system board for receiving the data generated by the microcontroller; and a computer system coupled to the ISD interface board, the computer system comprising an ISD software module for monitoring the data generated by the microcontroller.