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Arduino · current

Arduino UNO R3

ATmega328P-based Arduino board with 14 digital I/O, 6 analog inputs, USB-B and power jack.

Evidence: Inferred 4 sources · latest retrieved 2026-10-18 · audited

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Top view of an Arduino Uno R3 board with its USB-B socket, barrel jack and ATmega328P chip
Image: Suyash Dwivedi · CC BY-SA 4.0 · Wikimedia Commons

Key specs

Logic level
5 V Evidence: Documented
MCU
ATmega328P Evidence: Documented
CPU clock max
16 MHz Evidence: Documented
Sources disagree
Flash
32 KB Evidence: Documented
SRAM
2 KB Evidence: Documented
Digital IO pins
14 Evidence: Documented

Works with and related

Comparisons

Read the caveats · 1 source conflict

Suggested for: Compare boards: documented capabilities

All specifications 11
SpecValueEvidence
MCUATmega328PEvidence: Documented
CPU clock max16 MHz
16 MHz ceramic resonator (see conflicts[])
Source conflict (clock): 16 MHz (ceramic resonator) vs up to 20 MHz (ATmega328P CPU) – Board clock is 16 MHz per product page; datasheet 3.2 says up to 20 MHz, likely the MCU rating not the board. Our reading is inference. Audit: datasheet Features (p.2) also says 'AVR CPU at up to 16 MHz', so the datasheet is internally inconsistent; only section 3.2 says up to 20 MHz (ATmega328P rating). Board part Y1 is listed as ECS-160-20-4X-DU 'Oscillator' while the product page says 'ceramic resonator' (part-number decoding to 16 MHz is our unverified inference). Spec clock=16 MHz kept at class 1; conflict left open. RESOLVED 2026-10-18: Microchip DS40002061B rates the ATmega328P 0-20 MHz at 4.5-5.5 V (chip rating); board clock is 16 MHz (product page, datasheet Features). Chip maximum vs board clock are different quantities; datasheet 3.2 restates the chip rating. Residual unverified: Y1 part-number decoding.
Evidence: Documented
Flash32 KBEvidence: Documented
SRAM2 KBEvidence: Documented
Eeprom1 KBEvidence: Documented
Digital IO pins14
of which 6 PWM
Evidence: Documented
Analog inputs6Evidence: Documented
Input voltage max20 V
VIN pad 6-20 V per datasheet table 2.2
Evidence: Documented
Input voltage min6 V
VIN pad 6-20 V per datasheet table 2.2
Evidence: Documented
Operating voltage5 V
Board logic/power rail is 5 V (IOREF connected to 5V; +5V rail); datasheet has no row literally labelled operating voltage - reading is an inference
Evidence: Documented
USB connectorUSB-BEvidence: Documented
Caveats

logic_level_v=5 is supported by datasheet 5.1 JANALOG pin 2: 'IOREF - Reference for digital logic V - connected to 5V' (upgraded to class 1 by audit; previously class 2 inference from the regulator and ATmega328P rating). The datasheet power table does not give a maximum power consumption figure (the cell reads 'xx'). VIN 6-20 V is labelled 'Maximum input voltage from VIN pad' in datasheet 2.2, not a recommended operating range. Clock: board 16 MHz vs ATmega328P rating 20 MHz (resolved 2026-10-18, see conflicts[]).

Claims 4
Sources 4

How we verify