ATmega32U4 pinout

Package pin assignments for ATmega32U4, with peripheral signals, clock grades and a serial programming guide.

TQFP-44 44 contacts

QFN-44

45 contacts Current package

Microchip Technology · 44 numbered contacts. The underside pad appears below the contact map. See the individual package drawings for footprint dimensions.

32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM · 2.7–5.5 V · 16 MHz maximum · -40 to +85 °C

QFN-44 pinout

Top view · Pin 1 at the upper left · Schematic outline
EP is the exposed center pad on the underside.

Selected pin details

10 · PB2

Bidirectional · GPIO

General-purpose digital I/O. Alternate assignments: MOSI (SPI), PDI (SPI), PCINT2 (EXINT).

After reset · GPIO driver is high impedance during reset. Clock, debug, and alternate-function use depend on fuse and peripheral configuration.

7766J · Pinout and peripheral signal descriptions

Electrical limits · Link to this pin

All 45 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.
EP	EP Exposed pad	Exposed pad	Match the center pad to the 44PW mechanical drawing and the land-pattern guidance for the package.

Signal assignments

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

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

PE2 (33)

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

PE6 (1)

System clock

Review each signal assignment and the peripheral enable conditions in the data sheet. CLK0 → PC7

PC7 (32)

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-MU: 32 KiB flash · 2.5 KiB SRAM · 1 KiB EEPROM · 2.7–5.5 V · 16 MHz maximum · -40 to +85 °C
ATmega32U4RC-MU: 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.