Internal functions are functions that can be used without requiring any external library files. They are part of the PHPoC core. They can be divided into two main categories: PHP-based function and PHPoC function. Most of PHP-based functions are identical to standard PHP function. PHPoC function are additional functions which interact directly with hardware and peripherals (e.g. I/O, UART, I2C, SPI...). This document describes the meaning, syntax, parameter and return value of each internal function.