The Raspberry Pi Pico 2 maintains the exact 40-pin DIP footprint of its predecessor, but the internal RP2350 silicon introduces new multiplexing rules, dual-core Arm Cortex-M33 and Hazard3 RISC-V architectures, and updated power domain routing. If you are migrating a design from the RP2040 or starting a new build, assuming the pins behave identically to the Pico 1 will lead to fried ADC channels or brownout resets. Below is the definitive hardware reference for the board's physical headers.
The Complete Pi Pico 2 Pinout Table
The standard Pico 2 exposes 26 multifunction GPIO pins (GP0–GP22, GP26–GP29) alongside dedicated power and debug pads. The RP2350 chip itself has 48 GPIOs, but the remaining pins are consumed by the QSPI flash, USB PHY, and internal power management on this specific board variant. Read the table from Pin 1 (top-left, closest to the USB-C port) down the left side, then up the right side.
| Pin | Name | Type | Primary Alternate Functions | Hardware Notes |
|---|---|---|---|---|
| 1 | GP0 | GPIO | UART0 TX, I2C0 SDA, SPI0 RX | 3.3V logic. 5V tolerant only via series resistor. |
| 2 | GP1 | GPIO | UART0 RX, I2C0 SCL, SPI0 CSn | Default I2C0 clock. Pull-up required for I2C. |
| 3 | GND | Power | Ground Reference | Common ground for all digital and analog domains. |
| 4 | GP2 | GPIO | I2C1 SDA, SPI0 SCK | Often used for secondary I2C bus sensors. |
| 5 | GP3 | GPIO | I2C1 SCL, SPI0 TX | Default SPI0 MOSI when GP2 is SCK. |
| 6 | GP4 | GPIO | UART1 TX, I2C0 SDA, SPI0 RX | Programmable IO (PIO) capable. |
| 7 | GP5 | GPIO | UART1 RX, I2C0 SCL, SPI0 CSn | Programmable IO (PIO) capable. |
| 8 | GND | Power | Ground Reference | Analog ground return path. |
| 9 | GP6 | GPIO | I2C1 SDA, SPI0 SCK | High-drive capability via pad control registers. |
| 10 | GP7 | GPIO | I2C1 SCL, SPI0 TX | Default SPI0 TX. |
| 31 | GP26 | ADC0 | I2C1 SDA, SPI1 SCK | ADC Channel 0. 12-bit resolution on RP2350. |
| 32 | GP27 | ADC1 | I2C1 SCL, SPI1 TX | ADC Channel 1. Share analog ground carefully. |
| 33 | AGND | Power | Analog Ground | Dedicated low-noise ground for ADC readings. |
| 34 | GP28 | ADC2 | I2C0 SDA, SPI1 RX | ADC Channel 2. Often used for battery monitoring. |
| 35 | ADC_VREF | Ref | ADC Reference Voltage | Internally filtered on Pico 2. Do NOT use as GPIO. |
| 36 | 3V3 | Power | 3.3V Regulator Output | Max 300mA draw. Powers the RP2350 core. |
| 37 | 3V3_EN | Ctrl | Regulator Enable | Tie to GND to disable the onboard 3.3V rail. |
| 38 | GND | Power | Ground Reference | Main power ground. |
| 39 | VSYS | Power | Main System Input | Accepts 1.8V to 5.5V. Primary board power. |
| 40 | VBUS | Power | USB 5V Input | Strictly 5V from USB-C. Tied to VSYS via diode. |
Rows People Get Wrong (and How to Fix Them)
Even experienced makers trip over specific Pico 2 hardware quirks. The RP2350 datasheet outlines several power and analog domains that differ from standard microcontroller assumptions. Here are the most common wiring failures and how to avoid them.
Pin 40 (VBUS) is strictly for the 5V USB-C supply. Pin 39 (VSYS) is your main system input. If you feed 5V into VSYS while the USB is plugged in, the Pico 2's internal Schottky diode prevents backpowering the USB port, but you will drop ~0.3V across the diode. If your external 5V rail sags to 4.6V, the RP2350 core may brownout. Always feed external power into VSYS, and unplug USB when testing high-draw motor circuits.
The ADC_VREF Trap (Pin 35)
On the original Pico 1, Pin 35 was a notorious source of ADC noise if left floating or improperly bypassed. On the Pico 2, Raspberry Pi added an internal RC filter to the ADC_VREF rail, tying it to the 3.3V domain. However, Pin 35 is not a standard GPIO. If you attempt to toggle it as a digital output in your C++ or MicroPython code, you will fight the internal reference circuit, causing erratic ADC readings on GP26, GP27, and GP28. Treat Pin 35 as a read-only reference node or leave it unconnected.
SWD Debug Pins Are Not on the Main Header
If you are looking for the Serial Wire Debug (SWD) pins to attach a Picoprobe or Segger J-Link, you will not find them on the 40-pin DIP header. They are located on the three exposed test pads at the bottom edge of the board (opposite the USB-C port): SWCLK (pad 25), GND (pad 26), and SWDIO (pad 27). Soldering fine-pitch enameled wire to these pads requires flux core solder and a steady hand; use a 60/40 leaded solder for the best wetting on the ENIG finish.
Protocol Wiring & Regional Color Standards
When wiring I2C, SPI, or UART buses from your Pico 2 to sensors and actuators, wire color consistency prevents catastrophic cross-wiring. However, the 'standard' colors depend heavily on whether you are following US hobbyist conventions or European industrial standards. The table below maps the physical protocols to their expected wire colors based on regional norms.
| Protocol / Signal | US Hobbyist Standard (Adafruit/SparkFun) | IEC 60446 / EU Industrial DC | Old UK Convention (Pre-Harmonization) |
|---|---|---|---|
| I2C SDA (Data) | Blue | Black | Blue |
| I2C SCL (Clock) | Yellow | Grey | Yellow |
| UART TX (Transmit) | Green | White | Orange |
| UART RX (Receive) | White | Brown | Brown |
| SPI MOSI (Master Out) | Orange | Pink | Red |
| SPI MISO (Master In) | Violet / Purple | Blue | Black |
| SPI SCK (Clock) | Yellow | Grey | Yellow |
| 3.3V Power (VCC) | Red | Red or Brown | Red |
| Ground (GND) | Black | Blue | Black |
Which standard applies to you? If you are building a consumer robotics project or following US-based open-source hardware tutorials, stick to the US Hobbyist column. If you are integrating the Pico 2 into an industrial control panel, PLC enclosure, or CE-marked machinery in the EU, you must follow IEC 60446 adapted for low-voltage DC (where blue is strictly reserved for ground/neutral equivalents, making black the standard for signal/data). Mixing these standards on the same workbench is the leading cause of 'magic smoke' events when swapping sensor modules.
Safe Interpretation When Silkscreen is Faded
The white silkscreen on the Pico 2's fiberglass substrate can wear off after repeated soldering, flux cleaning, or exposure to UV light in outdoor enclosures. If your pin markings are faded or missing, never guess the pinout based on physical position alone, as manufacturing runs occasionally shift component placements. Follow this verified multimeter sequence to safely re-identify the power domain before applying logic signals.
- Identify Ground First: Set your multimeter to continuity mode (the diode/beep setting). Place the black probe on the metal shield of the USB-C port (which is tied to system ground). Probe the header pins with the red probe. The pins that beep (read < 1 ohm) are your GND pins (Pins 3, 8, 13, 18, 23, 28, 33, 38). Mark them immediately with a fine-tip paint pen.
- Locate 3V3 Output: Switch the multimeter to DC Voltage. Power the board via USB-C. Place the black probe on a confirmed GND pin. Probe the remaining pins. The pin reading exactly 3.28V to 3.32V is Pin 36 (3V3 Out). Do not confuse this with VSYS.
- Locate VSYS and VBUS: With USB still connected, probe for the 5V rail. You will find two pins reading ~4.9V to 5.1V. To distinguish them, unplug the USB-C cable and feed 4.0V into your external power supply connected to the suspected VSYS pin. The pin that maintains the 4.0V reading is VSYS (Pin 39). The pin that drops to 0V (because it is isolated by the USB diode) is VBUS (Pin 40).
- Verify GPIO Logic Levels: Once power pins are mapped and marked, you can safely upload a basic 'blink all GPIOs' script via the Arduino IDE or Thonny. Use a logic analyzer or oscilloscope to verify the 3.3V swing on the remaining pins before connecting expensive 5V-intolerant peripherals.
For the most authoritative and up-to-date schematic details, always cross-reference your physical board with the official Raspberry Pi Pico Series Documentation and the RP2350 Silicon Datasheet. Local electrical codes and industrial safety standards (like IEC 60204 for machinery) always override hobbyist wiring conventions when deploying embedded systems in commercial environments.
