# Digital Circuits 7: MCUs... how do they work? ## Overview ![](https://cdn-learn.adafruit.com/assets/assets/000/054/594/medium800/components_ATMEL_MEGA328P_AU_1328.jpg?1527599155) Above is a picture of the ATmega328 silicon die/chip. This is what's inside that large, long IC on many Arduino UNO compatibles and the small square IC on an [Adafruit Metro Classic](https://www.adafruit.com/product/2488 "Adafruit Metro Classic") (below) and on an Arduino pro mini. Both packages appear on a number of other comparable microcontroller boards. In this guide we'll take a tour of the '328, looking at each significant functional piece. This guide is going to be fairly high level, most of the concepts will be applicable to any microcontroller. For full details on the '328 see the [datasheet from Microchip](https://ww1.microchip.com/downloads/en/DeviceDoc/Atmel-7810-Automotive-Microcontrollers-ATmega328P_Datasheet.pdf) (note it is very long, technical, and sleep inducing). ![](https://cdn-learn.adafruit.com/assets/assets/000/054/601/medium800/components_2488-20.jpg?1527601623) - [Next Page](https://learn.adafruit.com/mcus-how-do-they-work/the-building-blocks.md) ## Featured Products ### Arduino bootloader-programmed chip (Atmega328P) [Arduino bootloader-programmed chip (Atmega328P)](https://www.adafruit.com/product/123) This is a preprogrammed Atmega328P chip, useful if you want to make your own Arduino-compatible or repair a damaged chip on an exisiting Arduino UNO, Duemilanove, Diecimila, or NG! This chip is programmed with 'ADAboot', my version of the bootloader that is... Out of Stock [Buy Now](https://www.adafruit.com/product/123) [Related Guides to the Product](https://learn.adafruit.com/products/123/guides) ### Adafruit METRO 328 Fully Assembled - Arduino IDE compatible [Adafruit METRO 328 Fully Assembled - Arduino IDE compatible](https://www.adafruit.com/product/50) We sure love the ATmega328 here at Adafruit, and we use them _a lot_ for our own projects. The processor has plenty of GPIO, Analog inputs, hardware UART SPI and I2C, timers and PWM galore - just enough for most simple projects. When we need to go small, we use a Out of Stock [Buy Now](https://www.adafruit.com/product/50) [Related Guides to the Product](https://learn.adafruit.com/products/50/guides) ### Arduino Pro Mini 328 - 5V/16 MHz [Arduino Pro Mini 328 - 5V/16 MHz](https://www.adafruit.com/product/2378) The Arduino Pro Mini is SparkFun's minimal design approach to Arduino.  It's essentially a 5v Arduino that runs an 16 MHz bootloader on a super small, super thin board.  There are no connectors attached - allowing you to add whatever connectors or wire you want without too... No Longer Stocked [Buy Now](https://www.adafruit.com/product/2378) [Related Guides to the Product](https://learn.adafruit.com/products/2378/guides) ### Adafruit Feather 328P - Atmega328P 3.3V @ 8 MHz [Adafruit Feather 328P - Atmega328P 3.3V @ 8 MHz](https://www.adafruit.com/product/3458) With this Feather we're getting a little nostalgic for the ATmega328P - the classic 'Arduino' chip - with this Adafruit Feather 328P running a 3.3V and 8 MHz. Feather is the new development board from Adafruit, and like it's namesake it is thin, light, and lets you fly! We... In Stock [Buy Now](https://www.adafruit.com/product/3458) [Related Guides to the Product](https://learn.adafruit.com/products/3458/guides) ### Adafruit Metro Mini 328 V2 - Arduino-Compatible - 5V 16MHz [Adafruit Metro Mini 328 V2 - Arduino-Compatible - 5V 16MHz](https://www.adafruit.com/product/2590) One of our star development boards is the  **Adafruit METRO Mini 328** , an excellent lil fellow that lets you make your Arduino-based project tiny.  Recently we had to redesign this board to move from the obsolete CP2104 to the available CP2102N, and one thing... In Stock [Buy Now](https://www.adafruit.com/product/2590) [Related Guides to the Product](https://learn.adafruit.com/products/2590/guides) ### DC Boarduino (Arduino compatible) Kit (w/ATmega328) [DC Boarduino (Arduino compatible) Kit (w/ATmega328)](https://www.adafruit.com/product/72) If you've ever struggled to use a solderless breadboard with an Arduino, you understand how frustrating it can be! This clone acts just like an Arduino, and works with the latest Arduino software. For many projects it can even be preferable! The kit includes all parts necessary, the... No Longer Stocked [Buy Now](https://www.adafruit.com/product/72) [Related Guides to the Product](https://learn.adafruit.com/products/72/guides) ## Related Guides - [Adafruit Feather 328P](https://learn.adafruit.com/adafruit-feather-328p-atmega328-atmega328p.md) - [Ladyada's Learn Arduino - Lesson #1](https://learn.adafruit.com/ladyadas-learn-arduino-lesson-number-1.md) - [DS1307 Real Time Clock Breakout Board Kit](https://learn.adafruit.com/ds1307-real-time-clock-breakout-board-kit.md) - [Reverse Geocache Box](https://learn.adafruit.com/reverse-geocache-engagement-box.md) - [Light Meter](https://learn.adafruit.com/light-meter.md) - [Arduino Lesson 15. DC Motor Reversing](https://learn.adafruit.com/adafruit-arduino-lesson-15-dc-motor-reversing.md) - [Adafruit Metro Mini](https://learn.adafruit.com/adafruit-metro-mini.md) - [FTDI Friend](https://learn.adafruit.com/ftdi-friend.md) - [LED Lightbox](https://learn.adafruit.com/led-lightbox.md) - [Animating Multiple LED Backpacks](https://learn.adafruit.com/animating-multiple-led-backpacks.md) - [Sending an SMS with Temboo](https://learn.adafruit.com/sending-an-sms-with-temboo.md) - [SMS Texting Pet Food Dish](https://learn.adafruit.com/sms-texting-pet-food-dish.md) - [RePaper eInk Development Board](https://learn.adafruit.com/repaper-eink-development-board.md) - [Halloween Pumpkin](https://learn.adafruit.com/halloween-pumpkin.md) - [Bluetooth Temperature & Humidity Sensor](https://learn.adafruit.com/bluetooth-temperature-and-humidity-sensor.md) - [Wave Shield Voice Changer](https://learn.adafruit.com/wave-shield-voice-changer.md)