pimoroni RP2040 Build HAT

AI context

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

BOARD: the Raspberry Pi Build HAT is an add-on board that fits any Raspberry Pi with a 40-pin GPIO header and drives up to four LEGO Technic motors and sensors from the LEGO Education SPIKE Portfolio, along with devices from the MINDSTORMS Robot Inventor kit and most other LEGO parts that use an LPF2 connector. An onboard RP2040 runs the firmware that handles the hard real-time LPF2 work, so the Pi never touches the device timing itself.
BUS: the HAT-to-Pi link is called the 'command port', a 115200 baud serial interface, 8 bits, no parity, one stop bit (8N1), with no flow control. The protocol is entirely plain text, so a terminal emulator on the Pi can drive the HAT by hand. The firmware numbers the four physical ports 0 to 3, and a 'port' command sets which one later commands address.
POWER: DC input is a 2.1 mm barrel jack, centre positive, 8 V plus or minus 10 per cent (7.2 to 8.8 V), fed by the Build HAT power supply or a 7.5 V battery pack. With that supply connected the HAT powers the Raspberry Pi itself (every model except Pi 400) as well as all connected devices. With no external supply the board still runs, but only for sensors - there is no motor power.
LPF2 DEVICE POWER: every port carries a +3.3 V logic supply that is always present, and a separate driver IC per port supplies about +7.2 V for motors and other high-power devices. Drawing too much from the 3.3 V rail raises a 'Port power fault' message for as long as the fault lasts; a fault on the motor rail raises 'Motor power fault' repeatedly, is latched in hardware and must be cleared explicitly (clear_faults) once the cause is removed. The drivers can output PWM of either polarity, so one setpoint carries both speed and direction.
CONTROL: each port has its own controller, in 'direct PWM' mode by default, where the setpoint is a number from -1 to +1 that maps straight to output power, or in 'PID' mode, where it reads a speed or angle value back from the device and adjusts power to track a setpoint. Some devices have to be powered very soon after they connect and in reverse, which is a setpoint of -1.
PINOUT: the 40-pin header, numbered as the Raspberry Pi numbers it - odd pads down one row, even pads down the other - as published on the pinout the vendor links: 1 3V3, 2 5V, 3 GPIO 2 (I2C1 SDA), 4 5V, 5 GPIO 3 (I2C1 SCL), 6 GND, 7 GPIO 4 (Reset), 8 GPIO 14 (UART0 TX), 9 GND, 10 GPIO 15 (UART0 RX), 11 GPIO 17 (CTS), 12 GPIO 18 (PCM CLK), 13 GPIO 27, 14 GND, 15 GPIO 22, 16 GPIO 23, 17 3V3, 18 GPIO 24, 19 GPIO 10 (SPI0 MOSI), 20 GND, 21 GPIO 9 (SPI0 MISO), 22 GPIO 25, 23 GPIO 11 (SPI0 SCLK), 24 GPIO 8 (SPI0 CE0), 25 GND, 26 GPIO 7 (SPI0 CE1), 27 GPIO 0 (EEPROM SDA), 28 GPIO 1 (EEPROM SCL), 29 GPIO 5, 30 GND, 31 GPIO 6, 32 GPIO 12 (PWM0), 33 GPIO 13 (PWM1), 34 GND, 35 GPIO 19 (PCM FS), 36 GPIO 16 (RTS), 37 GPIO 26, 38 GPIO 20 (PCM DIN), 39 GND, 40 GPIO 21 (PCM DOUT).
TRAPS: only four LPF2 ports exist, so a fifth motor means a second HAT. The Pi 400 needs a ribbon cable or extension because the HAT cannot sit on it. Motor power is gated on the barrel jack, so a project that 'works on USB' will not turn a motor. Motor-rail faults latch in hardware - power-cycling the motor does not clear them, clear_faults does.