Skip to content

Arduino hardware package for ATmega1284, ATmega644, ATmega324, ATmega324PB, ATmega164, ATmega32, ATmega16 and ATmega8535


Notifications You must be signed in to change notification settings


Folders and files

Last commit message
Last commit date

Latest commit


Repository files navigation


Build Status MegaCore forum thread

An Arduino core for ATmega8535, ATmega16, ATmega32, ATmega164, ATmega324, ATmega644 and ATmega1284, all running the Urboot bootloader. Most Arduino UNO-compatible libraries will work with this core. If not, it's fairly straightforward to port a library. This core requires at least Arduino IDE v1.6, where v1.8.9 or newer is recommended. IDE 2.x should also work.

From MightyCore version 3 and onwards, the Optiboot bootloader has been replaced by the superior Urboot bootloader. It's smaller, faster, and has automatic baud rate detection. Other cool features the bootloader provides but are not utilized by MightyCore are user program metadata stored in flash that (can easily be viewed by Avrdude -xshowall) and chip erase functionality. If you already have Optiboot installed and don't want to replace it with Urboot, you can still upload programs without any compatibility issues. However, if you're burning a bootloader to a new chip, Urboot is the way to go.

If you're looking for a great development board for these DIP-40 microcontrollers, I got you covered! I've used the Arduino UNO for years, but felt like vital functionality was missing on the board. When designing this board I made sure all missing functionality was added. The board can be bought on my Tindie store.
Read more in the hardware section below.

Table of contents

Supported microcontrollers

  • ATmega1284
  • ATmega644
  • ATmega324
  • ATmega164
  • ATmega32
  • ATmega16
  • ATmega8535

All variants - P, PA, A, PB. Select the correct version in the 'Variant' menu

Can't decide what microcontroller to choose? Have a look at the specification table below:

mega1284 mega644 mega324 mega164 mega32 mega16 mega8535
Flash 128kiB 64kiB 32kiB 16kiB 32kiB 16kiB 8kiB
RAM 16kiB 4kiB 2kiB 1kiB 2kiB 1kiB 0.5kiB
EEPROM 4kiB 2kiB 1kiB 0.5kiB 0.5kiB 0.5kiB 0.5kiB
Serial ports 2 2 2/3* 2 1 1 1
PWM pins 8 6 6/9* 6 4 4 4
IO pins 32 32 32/39* 32 32 32 32

* ATmega324PB has 3 serial ports, 9 PWM pins, and 39 IO pins if the internal oscillator is used.

Supported clock frequencies

MightyCore supports a variety of different clock frequencies. Select the microcontroller in the boards menu, then select the clock frequency. You will have to hit "Burn bootloader" in order to set the correct fuses and upload the correct bootloader. This also has to be done if you want to change any of the fuse settings (BOD and EEPROM settings) regardless if a bootloader is installed or not. Make sure you connect an ISP programmer, and select the correct one in the "Programmers" menu. For time-critical operations, an external crystal/oscillator is recommended. The Urboot bootloader has automatic baud rate detection, so UART uploads should work fine even though the oscillator is a little too fast or too slow.

Frequency Oscillator type Default upload speed
(bootloader has auto-baud)
16 MHz External crystal/oscillator 115200 Default clock on most AVR based Arduino boards
20 MHz External crystal/oscillator 115200
18.4320 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
14.7456 MHz  External crystal/oscillator 115200 Great clock for UART communication with no error
12 MHz External crystal/oscillator 57600
11.0592 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
9.216 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
8 MHz External crystal/oscillator 57600 Common clock when working with 3.3V
7.3728 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
6 MHz External crystal/oscillator 57600
4 MHz External crystal/oscillator 9600
3.6864 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
2 MHz External crystal/oscillator 9600
1.8432 MHz External crystal/oscillator 115200 Great clock for UART communication with no error
1 MHz External crystal/oscillator 9600
8 MHz Internal oscillator 38400 Might cause UART upload issues. See comment above
4 MHz Internal oscillator 9600 Derived from the 8 MHz internal oscillator
2 MHz Internal oscillator 9600 Derived from the 8 MHz internal oscillator
1 MHz Internal oscillator 9600 Derived from the 8 MHz internal oscillator

Bootloader option

MightyCore lets you select which serial port you want to use for uploading. UART0 is the default port for all targets, but ATmega324/644/1284 can also use UART1 for upload. If your application doesn't need or require a bootloader for uploading you can also choose to disable it by selecting No bootloader. This frees 384 bytes of flash memory on ATmega8535/16/32/164/324 and 512 bytes on ATmega644/1284.

Note that you need to connect a programmer and hit Burn bootloader if you want to change any of the Bootloader settings.

Baud rate option

Since Urboot has automatic baud rate detection, the upload baud rate can be changed without having to re-flash the bootloader. The default baud rate setting will pick a suited baud rate that also works with the legacy Optiboot bootloader used in earlier MightyCore versions. The other baud rate options may or may not work, depending on the clock frequency and accuracy of the clock source. A rule of thumb is that "non-round" baud rates like 230400 works best with "non-round" clock speeds like 18.4320 MHz, while "round" ones like 16 MHz work best with "round" baud rates like 250000.

BOD option

Brown-out detection, or BOD for short lets the microcontroller sense the input voltage and shut down if the voltage goes below the brown-out setting. To change the BOD settings you'll have to connect an ISP programmer and hit "Burn bootloader". Below is a table that shows the available BOD options:

ATmega1284 Atmega644 ATmega324 ATmega164 ATmega32 ATmega16 ATmega8535
4.3V 4.3V 4.3V 4.3V 4.0V 4.0V 4.0V
2.7V 2.7V 2.7V 2.7V 2.7V 2.7V 2.7V
1.8V 1.8V 1.8V 1.8V - - -
Disabled Disabled Disabled Disabled Disabled Disabled Disabled

EEPROM option

If you want the EEPROM to be erased every time you burn the bootloader or upload using a programmer, you can turn off this option. You'll have to connect an ISP programmer and hit "Burn bootloader" to enable or disable EEPROM retain. Note that when uploading using a bootloader, the EEPROM will always be retained.

Note that if you're using an ISP programmer or have the Urboot bootloader installed, data specified in the user program using the EEMEM attribute will be uploaded to EEPROM when you upload your program in Arduino IDE. This feature is not available when using the older Optiboot bootloader.

#include <avr/eeprom.h>

volatile const char ee_data EEMEM = {"Data that's loaded straight into EEPROM\n"};

void setup() {

void loop() {

Link time optimization / LTO

Link time optimization (LTO for short) optimizes the code at link time, usually making the code significantly smaller without affecting performance. You don't need to hit "Burn Bootloader" in order to enable or disable LTO. Simply choose your preferred option in the "Tools" menu, and your code is ready for compilation. If you want to read more about LTO and GCC flags in general, head over to the GNU GCC website!

Printf support

Unlike the official Arduino cores, MightyCore has printf support out of the box. If you're not familiar with printf you should probably read this first. It's added to the Print class and will work with all libraries that inherit Print. Printf is a standard C function that lets you format text much easier than using Arduino's built-in print and println. Note that this implementation of printf will NOT print floats or doubles. This is disabled by default to save space but can be enabled using a build flag if using PlatformIO.

If you're using a serial port, simply use Serial.printf(F("Milliseconds since start: %ld\n"), millis());. As you can see, printf supports the F() macro, but you don't have to use it. Other libraries that inherit the Print class (and thus support printf) are the LiquidCrystal LCD library and the U8G2 graphical LCD library.

Pin macros

Note that you don't have to use the digital pin numbers to refer to the pins. You can also use some predefined macros that map "Arduino pins" to the port and port number:

// Use PIN_PB0 macro to refer to pin PB0 (Arduino pin 0 with the standard and Sanguino pinout)
digitalWrite(PIN_PB0, HIGH);

// Results in the exact same compiled code
digitalWrite(0, HIGH);

Write to own flash

MightyCore uses the excellent Urboot bootloader, written by Stefan Rueger. Urboot supports flash writing within the running application, meaning that content from e.g. a sensor can be stored in the flash memory directly without needing external memory. Flash memory is much faster than EEPROM, and can handle at least 10,000 write cycles before wear becomes an issue. For more information on how it works and how you can use this in your own application, check out the Serial_read_write for a simple proof-of-concept demo, and Flash_get_put + Flash_iterate for useful examples on how you can store strings, structs, and variables to flash and retrieve then afterward.

PROGMEM with flash sizes greater than 64kiB

The usual PROGMEM attribute stores constant data such as string arrays to flash and is great if you want to preserve the precious RAM. However, PROGMEM will only store content in the lower section, from 0 and up to 64kiB. If you want to store data in the upper section, use PROGMEM1 (64 - 128kiB) if your target is an ATmega1284/P. Accessing this data is not as straightforward as with PROGMEM, but it's still doable:

const char far_away[] PROGMEM1 = "Hello from far away!\n"; // (64  - 128kiB)

void print_progmem()
  char c;

  // Print out far_away
  for(uint8_t i = 0; i < sizeof(far_away); i++)
    c = pgm_read_byte_far(pgm_get_far_address(far_away) + i);


This core has three different pinout options:

  • Standard: The default pinout, and is based on the original AVR pinout.
  • Bobuino: Basically an Arduino UNO pinout setting. This pinout version is great for use with shields or code that's written for the Arduino UNO, as the pin functions stay the same (MOSI on D11, MISO on D12, SCK on D13).
  • Sanguino: This pinout is common on older 3D printer controllers such as the Sanguino, RepRap Sanguinololu, and RepRap Gen7. This pinout is also known as "avr_developers".

Please have a look at the (pins_arduino.h) files for detailed info. Pick your favorite!

Click to enlarge:

MightyCore Standard pinout MightyCore Bobuino pinout MightyCore Sanguino pinout


Select your microcontroller in the boards menu, then select the clock frequency. You'll have to hit "Burn bootloader" in order to set the correct fuses and upload the correct bootloader.
Make sure you connect an ISP programmer, and select the correct one in the "Programmers" menu. For time-critical operations, an external oscillator is recommended.

How to install

Boards Manager Installation

This installation method requires Arduino IDE version 1.8.0 or greater.

  • Open the Arduino IDE.
  • Open the File > Preferences menu item.
  • Enter the following URL in Additional Boards Manager URLs:
  • Open the Tools > Board > Boards Manager... menu item.
  • Wait for the platform indexes to finish downloading.
  • Scroll down until you see the MightyCore entry and click on it.
  • Click Install.
  • After installation is complete close the Boards Manager window.

Manual Installation

Click on the "Download ZIP" button. Extract the ZIP file, and move the extracted folder to the location "~/Documents/Arduino/hardware". Create the "hardware" folder if it doesn't exist. Open Arduino IDE and a new category in the boards menu called "MightyCore" will show up.

Arduino CLI Installation

Run the following command in a terminal:

arduino-cli core install MightyCore:avr --additional-urls


PlatformIO is an open-source ecosystem for IoT and embedded systems, and supports MightyCore.

See for more information.

Getting started with MightyCore

  • Hook up your microcontroller as shown in the pinout diagram.
    • If you're not planning to use the bootloader (uploading code using a USB to serial adapter), the FTDI header and the 100 nF capacitor on the reset pin can be omitted.
  • Open the Tools > Board menu item, select MightyCore and select your preferred target.
  • If the BOD option is presented, you can select at what voltage the microcontroller will shut down at. Read more about BOD here.
  • Select your preferred pinout. Personally, Standard is the most logical one; Bobuino is better for Arduino UNO pin compatibility. Read more about the different pinouts here.
  • Select your preferred clock frequency. 16 MHz is standard on most Arduino boards.
  • Select what kind of programmer you're using under the Programmers menu.
  • If the Variants option is presented, you'll have to specify what version of the microcontroller you're using. E.g the ATmega1284 and the ATmega1284P have different device signatures, so selecting the wrong one will result in an error.
  • Hit Burn Bootloader. The LED pin will not toggle after the bootloader has been loaded.
  • Disconnect the ISP programmer, and connect a USB to serial adapter to the target microcontroller shown in the pinout diagram. Select the correct serial port under the Tools menu, and click the Upload button. If you're getting a timeout error, it may be because the RX and TX pins are swapped, or the auto-reset circuit isn't working properly (the 100 nF capacitor and a 10k resistor on the reset line).

Your code should now be running on the microcontroller!

Wiring reference

To extend this core's functionality a bit further, I've added a few missing Wiring functions. As many of you know Arduino is based on Wiring, but that doesn't mean the Wiring development isn't active. These functions are used as "regular" Arduino functions, and there's no need to include an external library.
I hope you find this useful because they really are!

Function list

  • portMode()
  • portRead()
  • portWrite()
  • sleepMode()
  • sleep()
  • noSleep()
  • enablePower()
  • disablePower()

For more information please view the Wiring reference page

Library porting

Some users have reported issues when trying to use some 3rd party libraries with the ATmega8535, ATmega16, or ATmega32. A simple guide on how to port a library can be found here.


I've designed a development board for this particular core. I've added all the functionality I missed with the original Arduino boards and added the original AVR pinout. Not all supported microcontrollers have the same pin functions, and differences are highlighted. The boards measures 8.0 * 10.0 cm (3.15 * 3.94 in)
The development board has some additional unique features:

  • A voltage select jumper to run the microcontroller at 5V or 3.3V
  • A breadboard-friendly AVR with 32 IO pins, including 8 analog inputs
  • All pins located on the same side of the board, making it easy to hook it up to a breadboard
  • Male and female IO pin headers
  • Plenty of 5V, 3.3V, and GND points broken out, both male and female
  • A large ground pad on the underside of the board for connecting alligator clips, such as the ground clip of your oscilloscope
  • A potentiometer for use as a voltage reference (e.g. adjusting the LCD contrast)
  • Onboard LED connected to digital pin 0 (PB0)
  • A socketed crystal, perfect for experimenting with different clock frequencies
  • An auto reset enable header if you don't want the microcontroller to be reset every time you open the serial monitor on your PC
  • PWM pins clearly marked and a lookup table that can be found on the underside of the board (three ~ - all microcontrollers, two ~ - 164; 324; 644; 1284, one ~ - 1284)
  • IO peripherals are written on the underside of the board. No need to search in the datasheet anymore!
  • A Mini USB connector instead of a large USB Type-B plug
  • All serial handshake pins broken out for applications such as bit-banging (CTS, DTR, RI, DCD, DRT, RST)
  • JTAG header for programming and debugging (the JTAG enable fuse must be sat first)

The development board can be bought on my Tindie store. This includes a pre-programmed ATmega32 chip.

Click the images for full resolution

Development board front

Development board back

Bottom row

Minimal setup

Here is a simple schematic showing a minimal setup using an external crystal. Skip the crystal and the two capacitors if you're using the internal oscillator.
Click to enlarge:

DIP-40 package TQFP-44 SMD package ATmega324PB SMD package