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Pinout

The ATmega32u4 microcontroller has all the serial peripherals you would expect from a modern MCU, a full-speed USB connection and a generous number of ADC inputs. The image below shows all of the GPIO port and pin numbers of the MCU and the commonly used "Alternate functions" of each pin. The following sections below will describe in detail each category of pin funtions.

pinout description of all the alt functions of the atmega32u4 breakout board

danger

All GPIO and serial peripherals (except USB) operate at 3.3V. Level translators should be used when interfacing with other systems that may run at 1.8V or 5V

Power & GND​

The ATmega32u4 breakout board is capable of being powered in two ways:

  • The first being to connect a USB type C cable to the USB connector. This supplies 5V to the on board linear voltage regulator which then provides a 3.3V rail to the microcontroller. When connecting a USB cable 5V is also made availabe on the 5V pin header pin.
  • The second method is to provide 5V to the 5V pin. This will then supply the on board regulator which powers the 3v3 power rail. It is OK to use this method at the same time as plugging in a USB cable. A diode is in place to prevent back-feeding the 5V power rail into the USB connector.

Regardless of which method you choose to power the board, the 3.3V rail will be made available on the 3v3 pins.

caution

It is not recommended to supply 3.3V to the 3v3 pins as it could damage the on board linear voltage regulator.

GPIO​

Every GPIO can be used for reading in or writing out a signal and some also have the ability to trigger interrupts on Rising or Falling edges when configured as an input. The naming convention is [PORT_LETTER][PIN_NUMBER] - for example D5 is port D, pin 5.

Status LEDs​

The breakout board has three on board status LEDs.

  • 5V LED: Indiciates the status of the 5V rail
  • 3.3V LED: Indicates the status of the 3.3V rail
  • Status LED: General purpose LED that can be used in the user application. This LED is driven via the D4 GPIO.

Clock​

The breakout board has an on-board 16MHz crystal giving a final CORE_FREQ of 16MHz

USB​

USB Full-Speed capable of synchrounous serial communication at a frequency of 12MHz

TWI​

Two Wire Interface or I2c supports half-duplex serial communication to a max of 128 peripherals on a reduced two wire interface at a max frequency of 400kHz

  • SCL / D0: Serial Clock or GPIO D0
  • SDA / D1: Serial Data or GPIO D1

USART​

Universal Synchronous and Asynchronous Receiver and Transmitter supports full-duplex serial communication with hardware flow-control support

  • TX1 / D3: Transmit line or GPIO D3
  • RX1 / D2: Receive line or GPIO D2
  • CTS / D5: Flow Control - Clear to Send or GPIO D5
  • RTS / B7: Flow Control - Request to Send or GPIO B7

SPI​

Serial Peripheral Interface supports full-duplex serial communication to one or more peripherals at a max frequnecy of CORE_CLOCK_FREQ / 2 MHz

  • COPI / B2: Controller Out - Peripheral In or GPIO B2
  • CIPO / B3: Controler In - Peripheral Out or GPIO B3
  • SCK / B1: Serial Clock or GPIO B1
  • CS / B0: Chip Select or GPIO B0
note

The CS pin does not have to be used when utilizing the SPI peripheral. The user can instead manually actuate a GPIO pin connected to a peripherals CS line. This allows for a larger bus and more peripherals to be connected at once.

Analog​

The breakout board has twelve 10-bit ADC, or Analog to Digital Converter, pins. Each capable of reading in voltage ranges from 0 to 3.3V giving a reading accuracy down to ~3mV.

  • ADC0 / F0: Analog input 0 or GPIO F0
  • ADC1 / F1: Analog input 1 or GPIO F1
  • ADC4 / F4: Analog input 4 or GPIO F4
  • ADC5 / F5: Analog input 5 or GPIO F5
  • ADC6 / F6: Analog input 6 or GPIO F6
  • ADC7 / F7: Analog input 7 or GPIO F7
  • ADC8 / D4: Analog input 8 or GPIO D4
  • ADC9 / D6: Analog input 9 or GPIO D6
  • ADC10 / D7: Analog input 10 or GPIO D7
  • ADC11 / B4: Analog input 11 or GPIO B4
  • ADC12 / B5: Analog input 12 or GPIO B5
  • ADC13 / B6: Analog input 13 or GPIO B6

Special and Programming​

The special pins are generally used for programming the device via JTAG or USB DFU and are as follows

  • nRST: Active Low chip reset
  • nHWB: Active Low hardware boot. Used in conjuction with nRST to jump to the built-in bootloader
  • TCK: JTAG Clock
  • TMS: JTAG Test Mode Select
  • TDO: JTAG Test Data Out
  • TDI: JTAG Test Data In

AVR-SPI PROG header​

A dedicated programming header is available on the breakout board which matches the AVR-SPI standard programming pinout. These SPI pins are the same signals found down the left side of the board on GPIOs B1 - B3