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ATmega328P

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by adom

Microchip 8-bit AVR MCU, 28-pin DIP. 32 KB flash, 2 KB SRAM, 20 MHz, the Arduino Uno chip. Datasheet-verified.

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ATmega328P

Microchip Technology · 8-bit AVR MCU · PDIP-28

The 8-bit AVR microcontroller at the heart of the Arduino Uno, here in its classic 28-pin DIP. It packs 32 KB of self-programming flash, 2 KB SRAM, and 1 KB EEPROM, and runs the AVR RISC core at up to 20 MHz from 1.8 to 5.5 V. The 28-pin package brings out 23 GPIO across three ports, a 6-channel 10-bit ADC, three timer/counters with PWM, and hardware USART, SPI, and I2C (TWI). A ceramic resonator or crystal on XTAL1/XTAL2 sets the clock, or the internal 8 MHz RC oscillator frees both pins. Datasheet-verified 28-pin pinout.

Pinout

Pin Name Type Function
1 PC6/RESET/PCINT14 bidirectional Active-low reset input (when RSTDISBL fuse is unprogrammed); a low pulse longer than the minimum length generates a reset even without clock. If RSTDISBL is programmed, functions as PC6 GPIO (different electrical characteristics than other PC pins). Also PCINT14 pin-change interrupt source.
2 PD0/RXD/PCINT16 bidirectional Port D bit 0. Alternate functions: RXD (USART receive input), PCINT16 pin-change interrupt.
3 PD1/TXD/PCINT17 bidirectional Port D bit 1. Alternate functions: TXD (USART transmit output), PCINT17 pin-change interrupt.
4 PD2/INT0/PCINT18 bidirectional Port D bit 2. Alternate functions: INT0 external interrupt, PCINT18 pin-change interrupt.
5 PD3/INT1/OC2B/PCINT19 bidirectional Port D bit 3. Alternate functions: INT1 external interrupt, OC2B (Timer/Counter2 compare output B / PWM), PCINT19 pin-change interrupt.
6 PD4/T0/XCK/PCINT20 bidirectional Port D bit 4. Alternate functions: T0 (Timer/Counter0 external counter input), XCK (USART external clock), PCINT20 pin-change interrupt.
7 VCC power_in Digital supply voltage. Operating range 1.8V-5.5V (speed-grade dependent: 20MHz requires 4.5-5.5V, 10MHz at 2.7V, 4MHz at 1.8V).
8 GND power_in Ground reference. Tie together with pin 22 GND and the AVCC ground return.
9 PB6/XTAL1/TOSC1/PCINT6 bidirectional Port B bit 6. Alternate functions: XTAL1 (input to inverting oscillator amplifier for external crystal/resonator), TOSC1 (Timer/Counter2 asynchronous oscillator input when AS2 in ASSR is set and internal RC oscillator selected), PCINT6 pin-change interrupt.
10 PB7/XTAL2/TOSC2/PCINT7 bidirectional Port B bit 7. Alternate functions: XTAL2 (output from inverting oscillator amplifier), TOSC2 (Timer/Counter2 asynchronous oscillator output), PCINT7 pin-change interrupt.
11 PD5/T1/OC0B/PCINT21 bidirectional Port D bit 5. Alternate functions: T1 (Timer/Counter1 external counter input), OC0B (Timer/Counter0 compare output B / PWM), PCINT21 pin-change interrupt.
12 PD6/AIN0/OC0A/PCINT22 bidirectional Port D bit 6. Alternate functions: AIN0 (analog comparator positive input), OC0A (Timer/Counter0 compare output A / PWM), PCINT22 pin-change interrupt.
13 PD7/AIN1/PCINT23 bidirectional Port D bit 7. Alternate functions: AIN1 (analog comparator negative input), PCINT23 pin-change interrupt.
14 PB0/ICP1/CLKO/PCINT0 bidirectional Port B bit 0. Alternate functions: ICP1 (Timer/Counter1 input capture), CLKO (divided system clock output when CKOUT fuse is programmed), PCINT0 pin-change interrupt.
15 PB1/OC1A/PCINT1 bidirectional Port B bit 1. Alternate functions: OC1A (Timer/Counter1 compare output A / PWM), PCINT1 pin-change interrupt.
16 PB2/SS/OC1B/PCINT2 bidirectional Port B bit 2. Alternate functions: SS (SPI slave-select input; also controls SPI master/slave mode via DDRB), OC1B (Timer/Counter1 compare output B / PWM), PCINT2 pin-change interrupt.
17 PB3/MOSI/OC2A/PCINT3 bidirectional Port B bit 3. Alternate functions: MOSI (SPI master-out/slave-in data), OC2A (Timer/Counter2 compare output A / PWM), PCINT3 pin-change interrupt. Also used for ISP programming (data in).
18 PB4/MISO/PCINT4 bidirectional Port B bit 4. Alternate functions: MISO (SPI master-in/slave-out data), PCINT4 pin-change interrupt. Also used for ISP programming (data out).
19 PB5/SCK/PCINT5 bidirectional Port B bit 5. Alternate functions: SCK (SPI bus clock), PCINT5 pin-change interrupt. Also used for ISP programming (clock).
20 AVCC power_in Analog supply voltage for the A/D converter, Port C (PC3:0) and (in TQFP/VQFN) ADC7:6. Must be externally connected to VCC even if the ADC is unused; if the ADC is used, connect through an LC low-pass filter for noise isolation.
21 AREF passive Analog reference input for the A/D converter. Bypass with a decoupling capacitor to GND; may be driven externally or internally selected via ADMUX (AVCC or 1.1V internal bandgap).
22 GND power_in Analog ground return (shared with digital GND). Tie to pin 8 GND.
23 PC0/ADC0/PCINT8 bidirectional Port C bit 0. Alternate functions: ADC0 (analog input channel 0, 10-bit), PCINT8 pin-change interrupt.
24 PC1/ADC1/PCINT9 bidirectional Port C bit 1. Alternate functions: ADC1 (analog input channel 1, 10-bit), PCINT9 pin-change interrupt.
25 PC2/ADC2/PCINT10 bidirectional Port C bit 2. Alternate functions: ADC2 (analog input channel 2, 10-bit), PCINT10 pin-change interrupt.
26 PC3/ADC3/PCINT11 bidirectional Port C bit 3. Alternate functions: ADC3 (analog input channel 3, 10-bit), PCINT11 pin-change interrupt.
27 PC4/ADC4/SDA/PCINT12 bidirectional Port C bit 4. Alternate functions: ADC4 (analog input channel 4, 10-bit), SDA (TWI/I2C data line), PCINT12 pin-change interrupt.
28 PC5/ADC5/SCL/PCINT13 bidirectional Port C bit 5. Alternate functions: ADC5 (analog input channel 5, 10-bit), SCL (TWI/I2C clock line), PCINT13 pin-change interrupt.

Key specifications

Parameter Value
Core 8-bit AVR RISC
Flash 32 KB (self-programming)
SRAM 2 KB
EEPROM 1 KB
Max clock 20 MHz
GPIO 23 (ports B/C/D)
ADC 6-channel 10-bit (DIP)
Serial USART + SPI + I2C (TWI)
Timers 3 (2x 8-bit, 1x 16-bit) with PWM
Supply voltage 1.8-5.5 V
Package PDIP-28 (SPDIP)

Ordering variants

  • ATmega328P-PU (PDIP-28, tube)
  • ATmega328P-PN (PDIP-28)

CAD (KiCad official)

  • Symbol: MCU_Microchip_ATmega:ATmega328P-P
  • Footprint: Package_DIP:DIP-28_W7.62mm
  • 3D model: DIP-28 (KiCad packages3D)
  • 3D model files: atmega328p-etched.step / atmega328p-etched.glb carry the MPN laser-etched on the die in a toggleable Adom.LaserEtch group (Fusion-ready); atmega328p.step / atmega328p.glb are the bare package body.

Provenance

Data extracted from the manufacturer datasheet, not a distributor listing:

  • Datasheet: Microchip Technology datasheet (653 pp, sha256 b9b9d83cda56a95d, retrieved 2026-08-17, tier: manufacturer)
  • Extractor: ds2sf (Claude). Every pin and dimension is cited to a datasheet page; it refuses to fabricate.
  • CAD: KiCad official libraries (CC-BY-SA 4.0).

Datasheet PDF