PIO on RP2040/RP2350: build your own peripheral (WS2812, 1-Wire, extra UARTs) instead of bit-banging

Programmable I/O (PIO) is the feature that sets RP-series chips apart. Each PIO block contains state machines that run small programs with precise timing, independently of the CPU cores.

When to reach for PIO

• A protocol with tight timing the chip has no hardware block for: WS2812/NeoPixel LEDs, 1-Wire, Manchester encoding, IR remote codes, HUB75 LED matrices.
• More of a standard interface than the hardware has: extra UARTs or SPI/I2C buses.
• Counting fast signals without CPU load: quadrature encoders.

Bit-banging these in C or MicroPython is fragile once interrupts, Wi-Fi or other work competes for the CPU. A PIO program keeps the timing no matter what the cores do.

Don't write it from scratch

The official pico-examples repository (PIO section) has working programs for:

• pio_ws2812 and pio_ws2812_parallel: WS2812 LED strips
• pio_onewire: 1-Wire library with a DS18B20 temperature sensor example
• pio_uart_rx, pio_uart_tx, pio_uart_dma: extra UARTs
• pio_spi_*, pio_i2c_bus_scan: SPI and I2C
• pio_quadrature_encoder: encoder counting
• pio_hub75, pio_st7789_lcd: displays
• hello_pio, pio_blink: the minimal starting points

MicroPython also exposes PIO (the Raspberry Pi pico-micropython-examples repository has a PIO section, e.g. a NeoPixel ring).

Tips

• State machines are a limited resource; count them when you combine several PIO-based drivers or libraries.
• Pair PIO with DMA for high data rates (see pio_uart_dma, pio_logic_analyser).