arduino ATSAMD21G18A MKR WiFi 1010

Part & documents

Headline part	ATSAMD21G18A
Data sheet	ATSAMD21G18A data sheet →
Source	store.arduino.cc/products/arduino-mkr-wifi-1010 →

Specs

MCU	Microchip SAMD21G18A (Arm Cortex-M0+ at up to 48 MHz) with a u-blox NINA-W102 Wi-Fi/Bluetooth module
Clock	48 MHz

Pinout

38 pads, as the vendor numbers them.

#	Name	Function	Signals
1	AREF	Header pad 1 (the vendor numbers the header connector 1-28): analogue reference	AREF
2	A0/DAC0	Header pad 2 (the vendor numbers the header connector 1-28): ADC in / DAC out, can be used as GPIO	A0, DAC0
3	A1	Header pad 3 (the vendor numbers the header connector 1-28): ADC in, can be used as GPIO	A1
4	A2	Header pad 4 (the vendor numbers the header connector 1-28): ADC in, can be used as GPIO	A2
5	A3	Header pad 5 (the vendor numbers the header connector 1-28): ADC in, can be used as GPIO	A3
6	A4/SDA	Header pad 6 (the vendor numbers the header connector 1-28): ADC in, I2C SDA, can be used as GPIO	A4, SDA
7	A5/SCL	Header pad 7 (the vendor numbers the header connector 1-28): ADC in, I2C SCL, can be used as GPIO	A5, SCL
8	A6	Header pad 8 (the vendor numbers the header connector 1-28): ADC in, can be used as GPIO	A6
9	D0	Header pad 9 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D0
10	D1	Header pad 10 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D1
11	D2/PWM	Header pad 11 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D2, PWM
12	D3/PWM	Header pad 12 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D3, PWM
13	D4/PWM	Header pad 13 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D4, PWM
14	D5/PWM	Header pad 14 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D5, PWM
15	D6	Header pad 15 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D6
16	D7	Header pad 16 (the vendor numbers the header connector 1-28): GPIO, can be used as PWM	D7
17	D8/MOSI	Header pad 17 (the vendor numbers the header connector 1-28): SPI MOSI, can be used as GPIO, can be used as PWM	D8, MOSI
18	D9/SCK	Header pad 18 (the vendor numbers the header connector 1-28): SPI SCK, can be used as GPIO, can be used as PWM	D9, SCK
19	D10/MISO	Header pad 19 (the vendor numbers the header connector 1-28): SPI MISO, can be used as GPIO	D10, MISO
20	D11/SDA	Header pad 20 (the vendor numbers the header connector 1-28): I2C SDA, can be used as GPIO	D11, SDA
21	D12/SCL	Header pad 21 (the vendor numbers the header connector 1-28): I2C SCL, can be used as GPIO	D12, SCL
22	D13/RX	Header pad 22 (the vendor numbers the header connector 1-28): USART RX, can be used as GPIO	D13, RX
23	D14/TX	Header pad 23 (the vendor numbers the header connector 1-28): USART TX, can be used as GPIO	D14, TX
24	RESETN	Header pad 24 (the vendor numbers the header connector 1-28): reset input	RESETN
25	GND	Header pad 25 (the vendor numbers the header connector 1-28): power ground	GND
26	+3V3	Header pad 26 (the vendor numbers the header connector 1-28): power out (the datasheet gives no description text)	+3V3
27	VIN	Header pad 27 (the vendor numbers the header connector 1-28): VIN power input	VIN
28	+5V	Header pad 28 (the vendor numbers the header connector 1-28): power out	+5V
29	VUSB	USB connector pad 1: power supply input; output if the board is powered via VUSB on the header	USB
30	D-	USB connector pad 2: USB differential data -	USB
31	D+	USB connector pad 3: USB differential data +	USB
32	ID	USB connector pad 4: selects host/device functionality	USB
33	GND	USB connector pad 5: supply ground	USB
34	+3V3	Debug test pad 1: power out	power/reset
35	SWD	Debug test pad 2: single wire debug data	debug
36	RESETN	Debug test pad 3: processor reset input	power/reset
37	SWCLK	Debug test pad 4: single wire debug clock	debug
38	GND	Debug test pad 5: power ground	power/reset

Buses

Bus	Signals	Pins	Voltage	Note
I2C ×2	SDA, SCL	A4/SDA, A5/SCL, D11/SDA, D12/SCL	3.3 V V	Two I2C pairs reach the header: A4 (SDA) with A5 (SCL), and D11 (SDA) with D12 (SCL). No documented on-board device address on either - the ATECC508 is on an internal bus.
SPI ×1	SCK, MISO, MOSI	D9/SCK, D10/MISO, D8/MOSI	3.3 V V	Header SPI is on D8/D9/D10. The NINA-W102's own SPI link to the processor is internal to the board.
UART ×1	RX, TX	D13/RX, D14/TX	3.3 V V	D13 is USART receive and D14 is USART transmit; Serial1 also carries the link to the NINA module internally on PB23/PA22.

Power

Input	USB (micro-B), or the headers, or a single-cell Li-ion/LiPo on the on-board BQ24195L charger
Input range	VIN absolute maximum -0.3 to 5.5 V; VUSB absolute maximum -0.3 to 5.5 V

Outputs

Rail	Rating	Note
3V3	3.3 V V	the board's logic rail, on header pad 26
+5V	5 V V	header pad 28 is tied through a jumper to the USB power input - not a regulator output

Notes

Pin numbers 1-28 are the vendor's own header numbering; this entry extends the run to the USB connector (29-33) and the debug footprint (34-38), naming the connector and vendor pad in every description. Labels are the 'Function' column of the datasheet's own text pin tables (5.1 USB, 5.2 Headers, 5.3 Debug), so no vision pass was needed. Arduino publishes no I2C address for the ATECC508 or the NINA module in this document, so addresses is empty; the header table leaves the description cell of pad 26 (+3V3) blank and names the charger BQ24195L.

AI context

Dense context for pasting into a model prompt — addresses, pinout, voltages, tolerances and the vendor's reference circuit.

PART: Arduino MKR WiFi 1010, SKU ABX00023 - an MKR-form-factor board built on a Microchip SAMD21G18A (Arm Cortex-M0+ at up to 48 MHz), with a u-blox NINA-W102 module for Wi-Fi and Bluetooth (the module is ESP32-based and ships with Arduino's pre-certified firmware) and an ATECC508 crypto chip. Like every MKR board it can be powered over USB, over the headers, or from a single-cell Li-ion/LiPo through the on-board BQ24195L charger.
PINOUT: two headers in MKR form factor, which the vendor numbers as one 28-pin connector: pad 1 AREF, 2 A0/DAC0, 3 A1, 4 A2, 5 A3, 6 A4/SDA, 7 A5/SCL, 8 A6, 9 D0, 10 D1, 11 D2/PWM, 12 D3/PWM, 13 D4/PWM, 14 D5/PWM, 15 D6, 16 D7, 17 D8/MOSI, 18 D9/SCK, 19 D10/MISO, 20 D11/SDA, 21 D12/SCL, 22 D13/RX, 23 D14/TX, 24 RESETN, 25 GND, 26 +3V3, 27 VIN, 28 +5V. This entry keeps that vendor numbering 1-28, then numbers the USB connector 29-33 (1 VUSB, 2 D-, 3 D+, 4 ID, 5 GND) and the debug footprint 34-38 (+3V3, SWD, RESETN, SWCLK, GND).
I2C: the default bus is on A4 (SDA) and A5 (SCL), with a second pair on D11 (SDA) and D12 (SCL); neither carries a documented on-board device address, so addresses is empty. The ATECC508 and the NINA-W102 hang off the processor's internal buses, not the headers.
SUPPLY: VIN and USB/VUSB absolute maximum is -0.3 V to 5.5 V on both. Board thermal limits -40 to +85 C. Arduino publishes no separate recommended VIN window for this board in the datasheet, only the absolute maximum and the note that USB feeds VIN through a Schottky into a DC-DC, so the effective USB floor rises with load.
LOGIC AND LIMITS: 3.3 V I/O only and NOT 5 V tolerant - the vendor states that connecting 5 V signals to this board will damage it. There is no on-board level shifting on the headers, so anything 5 V needs an external shifter.
INTERNAL WIRING: the SAMD21 reaches the NINA-W102 over SPI on PA12/PA13/PA14/PA15 (NINA GPIO12 / SPIV_DI / SPIV_CS / SPIV_CLK) and over UART on PB23 (Serial1 RX) and PA22 (Serial1 TX), with PA27 as NINA_GPIO0, PB08 as module reset and PA28 as NINA_ACK.
TRAPS: (1) the 5V pin does not supply voltage - it is connected through a jumper to the USB power input. (2) The battery charger has a minimum charge current of 512 mA, so check the cell can take it. (3) USB host mode works only when the board is powered from the VUSB pin and the jumper next to it is shorted. (4) Reflashing the NINA module with custom firmware invalidates the radio certification. (5) The datasheet names the charger BQ24195L, and its header table leaves the description of pad 26 (+3V3) blank.

Provenance

Every figure on this page was read from the 3 sources below and last checked on Oct 29, 2026.