Often, the easiest way to program a PIC is to remove it from its circuit and plug it into an appropriate programmer. However, when developing new projects, this can become a real chore and so professional developers use a range of tools that allow programming and even debugging without removing the micro from the application circuit. Microchip refers to this method of programming as In-Circuit Serial Programming (ICSP).

While not all low-cost programmers support in-circuit programming, some can be modified to do so. Hobby programmers are usually supplied as kits, so it is often possible to solder wires to appropriate places within the circuit for connection to the application circuit’s ICSP header. However, this method is not general to all programmers.

The method used here is to plug an adaptor into the socket on the programmer. The adaptor picks off the programming signals and makes then available for connection to the application circuit, just like a "real" ICSP programmer. The programmer still "thinks" it is programming a PIC in the socket, when in fact it is programming the PIC in the application circuit.

WARNING!  This adaptor was designed and tested for use with Microchip's PICSTART Plus programmer, which allows all PICs to be inserted with pin 1 alighned to pin 1 of the programming socket.  Some low-cost programmers lack this flexibility and require the smaller PICs to be inserted with pin 1 in some location other than the socket's pin 1. This unit will not work with this type of programmer!