The programmer mode simply programs, reads or erases the PIC including EEPROM & Config fuses.
The debugger uses special hardware found in many but not all PICs that will let you set breakpoints (stops) and single step through you program. You can view/modify SFRs and RAM. The ICD2 will install a small program in the last 1/4K of Flash memory and often use a byte or two of RAM.
IMHO it's an incredible tool.
Debuggers are becoming standard features in many microcontrollers.
But as MicroChip provide full circuit diagrams and the software for it, it's fairly easy (and much cheaper) to make a compatible clone - like the Inchworm and Inchworm+.
But as MicroChip provide full circuit diagrams and the software for it, it's fairly easy (and much cheaper) to make a compatible clone - like the Inchworm and Inchworm+.