ELEGOO UNO R3 microcontroller board is based on the ATmega328P and CH340C, 100% compatible with Arduino UNO R3. It has 14 digital input/output pins (of which 6 can be used as PWM outputs), 6 analog inputs, a 16 MHz ceramic resonator, a USB connection, a power jack, an ICSP header, and a reset button. It contains everything you need to support your microcontroller, including dedicated SCL, SDA and IOREF pins; just connect it to a computer with a USB cable or power it with an AC-to-DC adapter or battery to get started. The ATmega328P on the UNO R3 controller board is the same as the official Arduino UNO R3 board, and comes pre-programmed with a bootloader that allows you to upload new code to it without using an external hardware programmer. The ATmega328P has 32 KB (with 0.5 KB occupied by the bootloader). It also has 2 KB of SRAM and 1 KB of EEPROM (which can be read and written with the EEPROM library). The RX and TX LEDs on the board will flash when data is being transmitted via the USB-to-serial chip and USB connection to the computer. The ELEGOO UNO R3 puts SDA and SCL pins beside the AREF. Besides, there are two new pins placed near the RESET pin. One is the IOREF which allows the shields to adapt to the voltage provided by the board and the other one is reserved for future purposes. The ELEGOO UNO R3 works with all existing shields and can adapt to new shields that use these additional pins.