Raspberry Pi Pico (RP2040)

Fig. 1. Raspberry Pi Pico (RP2040), 2x20 castellated. Hover or tap a signal to light up every pin that carries it.

• Every GPIO is 3.3 V and none are 5 V tolerant.
• Peripheral mappings are not fixed: each pin lists the SPI/I2C/UART instance it can reach, and you pick one in software. Two pins on the same instance cannot be used for the same role at once.
• GPIO23, 24, 25 and 29 exist on the RP2040 but are not on the header, they drive the SMPS mode, VBUS sense, the on-board LED and VSYS sense. On the Pico W they are taken over by the wireless chip, which is why the LED moves to the CYW43 on that model.
• VSYS (pin 39) accepts 1.8-5.5 V and feeds the on-board buck-boost regulator. VBUS (pin 40) is USB 5 V directly.
• ADC_VREF (pin 35) is a filtered 3.3 V reference; tie analog grounds to AGND (pin 33), not a digital GND pin, for quieter readings.
• The Pico 2 uses the same header and the same GP numbers on an RP2350: more RAM, a choice of Arm or RISC-V cores, and 12 PWM slices instead of 8.

• Drive a pin and read one

  Pico SDK

  #include "pico/stdlib.h"
  
  #define LED 25                 /* on-board LED, not on the header */
  
  gpio_init(LED);
  gpio_set_dir(LED, GPIO_OUT);
  gpio_put(LED, 1);
  
  gpio_init(15);
  gpio_set_dir(15, GPIO_IN);
  gpio_pull_up(15);              /* pulls are off until you ask */
  
  if (!gpio_get(15)) {
  }

  gpio_init resets the pin to SIO and clears both pulls, so call it before set_dir, not after. On a Pico W the LED is on the wireless chip and GPIO 25 does nothing.

Table 1. Pin assignments.