AVR microcontrollers feature one or more interfaces for programming or debugging. In-System Programming (ISP) is a programming interface used for programming the Flash, EEPROM, Lock bits, and Fuse bits in almost all AVR devices. This feature makes it possible to program the AVR microcontroller in the last stage of production of a target application board, reprogram if SW bugs are identified late in the process, or update the AVR device in the field, if required. Some ISP interfaces may also be used for on-chip debugging. It is therefore recommended to design the target application board so that the ISP connectors are easily accessible.