SPI peripheral
Use SCK, MOSI, MISO and a chip-select line. Firmware selects direction and clock phase. Check the separate ISP mapping when programming. SS → PB0 · SCK → PB1 · MOSI → PB2 · PDI → PB2 · MISO → PB3 · PDO → PB3
ATmega32U4 pinout
Package pin assignments for ATmega32U4, with peripheral signals, clock grades and a serial programming guide.
TQFP-44
44 contacts Current packageQFN-44 45 contacts
32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM · 2.7–5.5 V · 16 MHz maximum · -40 to +85 °C
TQFP-44 pinout
TQFP-44
36 · PF7
General-purpose digital I/O. Alternate assignments: TDI (JTAG), ADC7 (ADC).
After reset · GPIO driver is high impedance during reset. Clock, debug, and alternate-function use depend on fuse and peripheral configuration.
All 44 pins
| Pin | Signal | Direction | Function |
|---|---|---|---|
| 1 | PE6 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: INT6 (EXINT), AIN0 (AC). |
| 2 | UVCC Supply | Supply | USB pad regulator supply. Follow the power scheme for the intended USB mode. |
| 3 | DM Bidirectional | Bidirectional | Negative USB data line. Route as part of the USB differential pair. |
| 4 | DP Bidirectional | Bidirectional | Positive USB data line. Route as part of the USB differential pair. |
| 5 | UGND Return | Return | USB transceiver ground. Connect to the board ground return. |
| 6 | UCAP Regulator output | Regulator output | USB regulator capacitor terminal. Use a 1 µF capacitor to USB ground in the internal regulator configuration. |
| 7 | VBUS Input | Input | USB bus voltage monitor. Use the data sheet’s USB connection for bus or self-powered operation. |
| 8 | PB0 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: SS (SPI), PCINT0 (EXINT). |
| 9 | PB1 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: SCK (SPI), PCINT1 (EXINT). |
| 10 | PB2 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: MOSI (SPI), PDI (SPI), PCINT2 (EXINT). |
| 11 | PB3 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: MISO (SPI), PDO (SPI), PCINT3 (EXINT). |
| 12 | PB7 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: RTS (USART1), OCA (TC0), OCC (TC1), PCINT7 (EXINT). |
| 13 | RESET Input | Input | Active-low reset input. The in-system programmer uses this pin to enter serial programming mode. |
| 14 | VCC Supply | Supply | Digital supply. Connect every VCC pin and place a local 100 nF ceramic bypass close to each VCC-to-ground pair. |
| 15 | GND Return | Return | Supply return. Connect every ground pin. |
| 16 | XTAL2 Output | Output | Oscillator amplifier output. Follow the selected clock mode before attaching a circuit. |
| 17 | XTAL1 Input | Input | Oscillator amplifier input or external clock input, depending on clock fuses. |
| 18 | PD0 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: OCB (TC0), INT0 (EXINT), SCL (TWI). |
| 19 | PD1 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: INT1 (EXINT), SDA (TWI). |
| 20 | PD2 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: RXD (USART1), INT2 (EXINT). |
| 21 | PD3 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: TXD (USART1), INT3 (EXINT). |
| 22 | PD5 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: XCK (USART1), CTS (USART1). |
| 23 | GND Return | Return | Supply return. Connect every ground pin. |
| 24 | AVCC Supply | Supply | Analog supply. Connect it to the supply even if analog conversion is unused. Follow the data sheet’s filtering guidance for precision conversion. |
| 25 | PD4 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: ICP (TC1), ADC8 (ADC). |
| 26 | PD6 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: T (TC1), _OCD (TC4), ADC9 (ADC). |
| 27 | PD7 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: T (TC0), OCD (TC4), ADC10 (ADC). |
| 28 | PB4 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: PCINT4 (EXINT), ADC11 (ADC). |
| 29 | PB5 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: OCA (TC1), _OCB (TC4), PCINT5 (EXINT), ADC12 (ADC). |
| 30 | PB6 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: OCB (TC1), OCB (TC4), PCINT6 (EXINT), ADC13 (ADC). |
| 31 | PC6 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: OCA (TC3), _OCA (TC4). |
| 32 | PC7 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: ICP (TC3), OCA (TC4), CLK0 (CPU). |
| 33 | PE2 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: HWB (BOOT_LOAD). |
| 34 | VCC Supply | Supply | Digital supply. Connect every VCC pin and place a local 100 nF ceramic bypass close to each VCC-to-ground pair. |
| 35 | GND Return | Return | Supply return. Connect every ground pin. |
| 36 | PF7 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: TDI (JTAG), ADC7 (ADC). |
| 37 | PF6 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: TDO (JTAG), ADC6 (ADC). |
| 38 | PF5 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: TMS (JTAG), ADC5 (ADC). |
| 39 | PF4 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: TCK (JTAG), ADC4 (ADC). |
| 40 | PF1 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: ADC1 (ADC). |
| 41 | PF0 Bidirectional | Bidirectional | General-purpose digital I/O. Alternate assignments: ADC0 (ADC). |
| 42 | AREF Analog reference | Analog reference | ADC voltage reference terminal. Check the reference selection before driving this pin from an external voltage. |
| 43 | GND Return | Return | Supply return. Connect every ground pin. |
| 44 | AVCC Supply | Supply | Analog supply. Connect it to the supply even if analog conversion is unused. Follow the data sheet’s filtering guidance for precision conversion. |
Signal assignments
USART1 · Serial
Use TXD and RXD for asynchronous serial. XCK is for synchronous mode. The signal levels follow the microcontroller supply domain. TXD → PD3 · RXD → PD2 · XCK → PD5 · RTS → PB7 · CTS → PD5
Boot selection
Review each signal assignment and the peripheral enable conditions in the data sheet. HWB → PE2
Timer/Counter 0
Review each signal assignment and the peripheral enable conditions in the data sheet. T → PD7 · OCB → PD0 · OCA → PB7
Timer/Counter 1
Review each signal assignment and the peripheral enable conditions in the data sheet. T → PD6 · ICP → PD4 · OCA → PB5 · OCB → PB6 · OCC → PB7
Timer/Counter 3
Review each signal assignment and the peripheral enable conditions in the data sheet. ICP → PC7 · OCA → PC6
Timer/Counter 4
Review each signal assignment and the peripheral enable conditions in the data sheet. _OCA → PC6 · OCA → PC7 · _OCB → PB5 · OCB → PB6 · _OCD → PD6 · OCD → PD7
JTAG
Check the JTAG fuse and enable state before using the pins for GPIO. JTAG uses TCK, TMS, TDI and TDO. TCK → PF4 · TMS → PF5 · TDO → PF6 · TDI → PF7
External interrupts
Review each signal assignment and the peripheral enable conditions in the data sheet. PCINT0 → PB0 · PCINT1 → PB1 · PCINT2 → PB2 · PCINT3 → PB3 · PCINT4 → PB4 · PCINT5 → PB5 · PCINT6 → PB6 · PCINT7 → PB7 · INT0 → PD0 · INT1 → PD1 · INT2 → PD2 · INT3 → PD3 · INT6 → PE6
TWI / I²C
Connect SDA and SCL to the bus with pull-ups to a voltage supported by all devices. Verify the pull-up value for the bus capacitance and rate. SDA → PD1 · SCL → PD0
Analog-to-digital converter
Select the analog channel and reference in firmware. The reference choice and supply constrain the input range. ADC0 → PF0 · ADC1 → PF1 · ADC4 → PF4 · ADC5 → PF5 · ADC6 → PF6 · ADC7 → PF7 · ADC8 → PD4 · ADC9 → PD6 · ADC10 → PD7 · ADC11 → PB4 · ADC12 → PB5 · ADC13 → PB6
Analog comparator
Review each signal assignment and the peripheral enable conditions in the data sheet. AIN0 → PE6
System clock
Review each signal assignment and the peripheral enable conditions in the data sheet. CLK0 → PC7
USB device
Use the differential data pair and the USB pad supply and regulator network. See the manufacturer circuit for the chosen supply mode.
Electrical limits
| Parameter | Limit | Conditions and source |
|---|---|---|
| Supply and clock grade2.7–5.5 V · 16 MHz maximum | 2.7–5.5 V · 16 MHz maximum | Up to 8 MHz at 2.7 V and 16 MHz at 4.5 V. USB clock and voltage requirements depend on the selected operating mode. 7766J · Speed grades and ordering information |
| Ambient temperature grade-40 to +85 °C | -40 to +85 °C | For this order code. Verify silicon revision and errata in the current manufacturer documentation. 7766J · Ordering information |
| Program flash32 KiB | 32 KiB | Nonvolatile program memory. 7766J · Memory |
| SRAM2.5 KiB | 2.5 KiB | Volatile data and stack storage. 7766J · Memory |
| EEPROM1 KiB | 1 KiB | Nonvolatile data storage. 7766J · Memory |
| Clock and supplyOrder-code dependent | Order-code dependent | Use the grade table and the device’s speed-versus-voltage curve. 7766J · Electrical Characteristics |
Models and documents
Each package lists the documented order codes and variants covered by this map. Select the marked model to see its peripheral assignments and memory. Check the exact order code and datasheet revision before laying out a PCB.
- ATmega32U4
- 32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM. Choose the marked order code for voltage, clock, and temperature.
- ATmega32U4-AU
- 32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM · 2.7–5.5 V · 16 MHz maximum · -40 to +85 °C
- ATmega32U4RC-AU
- 32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM · 2.7–5.5 V · 16 MHz maximum · -40 to +85 °C
- ATmega32U4 data sheet· 7766J · Pin configuration, electrical characteristics, ordering table and serial programming.
- ATmega_DFP Device Family Pack· Machine-readable device definition: package contacts, peripheral routes, and memory sizes.
- AVR Microcontroller Hardware Design Considerations· Power supply, reset network, and programmer connection guidance.
- ATmega32U4 documentation and errata· Check current manufacturer documentation, ordering status and silicon revision applicability.
- AVR source register· Source identifiers, applicability, retrieval dates, and SHA-256 digests.