Verified 2026-10

Seeed Studio XIAO SAMD21 (Pre-Soldered) - Seeeduino XIAO

Mini Arduino-compatible module: Microchip ATSAMD21G18A Arm Cortex-M0+ at 48 MHz with 256 KB flash and 32 KB SRAM, 14 edge pads (11 digital, 11 analog, 10 PWM, one DAC) in the 21 x 17.8 mm XIAO footprint, powered and programmed over USB-C.

Place this board on a carrier in the editor →

Logic level3.3 V

Specs

MCU	Microchip ATSAMD21G18A-MU (Arm Cortex-M0+, up to 48 MHz)

Pinout

14 pads, as the vendor numbers them.

#	Name	Function	Signals
1	D0	GPIO, ADC AIN0, DAC output; no hardware PWM	GPIO, ADC AIN0, DAC, PA02
2	D1	GPIO, ADC AIN4	GPIO, ADC AIN4, PA04
3	D2	GPIO, ADC AIN18	GPIO, ADC AIN18, PA10
4	D3	GPIO, ADC AIN19	GPIO, ADC AIN19, PA11
5	D4	GPIO, ADC AIN16, I2C data	GPIO, ADC AIN16, I2C SDA, PA08
6	D5	GPIO, ADC AIN17, I2C clock	GPIO, ADC AIN17, I2C SCL, PA09
7	D6	GPIO, ADC AIN2, UART transmit	GPIO, ADC AIN2, UART TX, PB08
8	D7	GPIO, ADC AIN3, UART receive	GPIO, ADC AIN3, UART RX, PB09
9	D8	GPIO, ADC AIN7, SPI clock	GPIO, ADC AIN7, SPI SCK, PA07
10	D9	GPIO, ADC AIN5, SPI data in	GPIO, ADC AIN5, SPI MISO, PA05
11	D10	GPIO, ADC AIN6, SPI data out	GPIO, ADC AIN6, SPI MOSI, PA06
12	3V3_OUT	3.3 V power output	3.3 V rail
13	GND	Ground
14	VBUS	USB 5 V — power in or out	5 V

Buses

Bus	Signals	Pins	Voltage	Note
I2C ×1	SDA, SCL	D4, D5	3.3 V
SPI ×1	SCK, MISO, MOSI	D8, D9, D10	3.3 V
UART ×1	TX, RX	D6, D7	3.3 V
USB ×1	D+, D-			USB-C; supplies power and downloads code, native USB on the SAMD21
SWD ×1	SWCLK, SWDIO			debug pads outside the 14-pin edge pattern

Power

Input	USB-C 5 V (VBUS)
Input range	5 V

Seeed's table for this variant lists BAT input as not supported — there is no battery management and no charging on the SAMD21 XIAO, unlike the XIAO SAMD21 Plus. No typical current draw is published for the board.

Outputs

Rail	Rating	Note
3V3_OUT	3.3 V

Notes

Pin numbers are the vendor's own: Seeed's XIAO-SAMD21-DIP footprint and their KiCad symbol both number pads 1-7 as D0-D6 and 8-14 as D7, D8, D9, D10, 3V3_OUT, GND, VBUS — the same 2x7 geometry the existing XIAO ESP32-C3 part uses, and independently confirmed by the XIAO socket pin order in Seeed's own carrier schematics. D0 is the only pin with no hardware PWM (Seeed states 10 PWM channels, D1-D10); the SMD symbol carries six further pads (SWDIO, SWCLK, EN, GND, VIN, GND) for the underside castellations, so SWD and a VIN pad exist outside this edge pattern even though the same table says BAT input is unsupported — not resolved here. This is the base SAMD21, not the 30-pin XIAO SAMD21 Plus. Plain (no-header) and 3-pack SKUs are the same board; the pre-soldered one is the variant that mates with the female headers on the carriers.

Provenance

Every figure on this page was read from the 4 sources below and last checked on Oct 15, 2026.