OVERVIEW
The devices can be programmed using either the high voltage In-Circuit Serial Programming™ (ICSP™) method or the low-voltage ICSP™ method.
When using low-voltage ICSP™ programming (LVP = 1), the ICSPDAT/ICSPCLK functions are additionally enabled on the RA0/RA1 port pins. This legacy programming feature provides compatibility support for existing PIC18F1XK50 designs. For new designs, using the ICSPDAT/ICSPCLK functions on the RC0/RC1 port pins is recommended.

Hardware Requirements
HIGH-VOLTAGE ICSP PROGRAMMING
In High-Voltage ICSP™ mode, these devices require two programmable power supplies: one for VDD and one for the MCLR/VPP pin.

LOW-VOLTAGE ICSP PROGRAMMING
In Low-Voltage ICSP™ mode, these devices can be programmed using a single VDD source in the operating range. The MCLR/VPP pin does not have to be brought to a different voltage, but can instead be left at the normal operating voltage.

Single-Supply ICSP Programming
The LVP bit in Configuration Word 2 enables single supply (low-voltage) ICSP programming. The LVP bit defaults to a ‘1’ (enabled) from the factory. The LVP bit may only be programmed to ‘0’ by entering the High Voltage ICSP mode, where the MCLR/VPP pin is raised to VIHH. Once the LVP bit is programmed to a ‘0’, only the High-Voltage ICSP mode is available and only the High-Voltage ICSP mode can be used to program the device.