Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.
on chip debugger is sometimes also called as "in circuit debugger".
It uses JTAG interface of the hardware to debug the software written to the hardware.
In microcontroller(or microprocessor), suppose that you have written a program and u want to test on the hardware directly then you can use this "in circuit debugger" facility. With this you can run the instruction step by step in microcontroller itself. If code is wrong somewhere you will see unexpected results and you can track the fault in code easily. Thus on chip debugger is very much usefull for embedded controller programers.