Even though many microcontrollers offer an on-chip brown-out function, it may be desirable to use an external voltage supervisor. Many standard microcontrollers are Flash memory devices, which can be programmed in-circuit. Typically, to enter the in-circuit programming mode, some non-typical state needs to be forced. For PICmicro microcontrollers, the mode is called In-Circuit Serial Programming (ICSP). ICSP can be used to program the device after assembly, as well as for firmware updates in the field. This technical brief will show how the MCP111 and MCP121 may be used in PICmicro microcontroller systems where ICSP is required.