Power

• VB (VBUS) - This is the micro-USB input voltage, connected to the micro-USB port on the Raspberry Pi Pico. It is nominally 5V.
• VS (VSYS) - This is the main system input voltage. It can range from 1.8V to 5.5V and is used to generate the 3.3V needed for the RP2040 and the GPIO pins.
• EN (3V3_EN) - This connects to the enable pin on the Raspberry Pi Pico, and is pulled high (to VSYS) via a 100kΩ resistor.
• 3V - This is the 3.3V output from the Raspberry Pi Pico.
• VR (ADC_VREF) - This is the ADC power supply and reference voltage. It is generated on the Raspberry Pi Pico by filtering the 3.3V supply. It can be used with an external reference when ADC performance is required.
• G - This is the common ground for power and logic. All GND pins are highlighted in white on the silk, with the exception of the ground pin for the CAN Bus terminal block. It is labeled - (minus sign).

I2C Logic

• SCL - I2C clock pin on the PiCowbell. It is connected to your microcontroller I2C clock line, which is GPIO5 on the Pico. This connection is shared with the STEMMA QT port on the end of the board.
• SDA - I2C data pin on the PiCowbell. It is connected to your microcontroller I2C data line, which is GPIO4 on the Pico. This connection is shared with the STEMMA QT port on the end of the board.
• STEMMA QT - These connectors allow you to connect to dev boards with STEMMA QT connectors or to other things with various associated accessories. The port is located on the end of the PiCowbell.

Duplicate GPIO Hole Pads

The following pads on the PiCowbell CAN Bus have a duplicate hole pad next to it for solder-jumpering:

• GP0-GP15, GP16-GP22, Reset, A0-A2, VR, 3V, EN, VS and VB. Ground pins that have a duplicate hole pad are highlighted in white on the board silkscreen.
  • Note that GP20 and GP21 are connected by default to CAN Bus CS and INT. They can be disconnected from these GPIO pins by cutting the CS and INT jumpers described below.

Reset Button

In the center of the board, to the right of the STEMMA QT connector, is the reset button. It is routed to the reset pin on the PiCowbell and is labeled RST on the board silk. You can press it to restart your program.

Terminal Block Pins

On the front of the board is the terminal block with the three pins for communicating with the CAN Bus standard.

• L - the CAN low signal for the CAN Bus standard.
• - - common ground shared between the two CAN connections
• H - the CAN high signal for the CAN Bus standard.

Both L and H are connected to a 5V charge-pump voltage generator. Even if you are using 3.3V logic on a Pico board, it will generate a nice clean 5V as required by the CAN Bus transceiver.

Terminator Jumper

The terminator jumper is located on the front of the board, to the left of the terminal block. It is labeled Term and is outlined in white on the board silk.

• Term - The board has a 120 ohm termination resistor connected between H and L. You can disable (remove) the resistor by cutting the Term jumper, if your bus is already terminated.

MCP2515 Reset Pin and Jumper

• Reset Jumper - located on the back of the board, below the PiCowbell icon on the board silk, is the reset jumper. It is outlined in white on the board silk. You can cut this jumper to disconnect the MCP2515 reset pin from the Pico reset pin.
• Reset Pin - located on the front of the board to the right of the reset button. It is labeled RST on the silk. If you cut the reset jumper, you can use this pin to connect the MCP2515 reset pin to a different IO pin.

Chip Select Pin and Jumper

• CS Jumper - located on the back of the board, next to PiCowbell pin 20, is the chip select jumper. It is labeled CS and is outlined in white on the board silk. By default, the MCP2515 chip select pin is connected to GPIO20 on the PiCowbell. You can cut this jumper to disconnect the MCP2515 CS pin from PiCowbell pin 20.
• CS pin - located on the front of the board to the right of the reset button. It is labeled CS on the silk. If you cut the CS jumper, you can use this pin to connect the MCP2515 CS pin to a different IO pin.

Interrupt Pin and Jumper

• INT Jumper - located on the back of the board, next to PiCowbell pin 21, is the interrupt jumper. It is labeled INT and is outlined in white on the board silk. By default, the MCP2515 interrupt pin is connected to GPIO21 on the PiCowbell. You can cut this jumper to disconnect the MCP2515 INT pin from PiCowbell pin 21.
• INT pin - located on the front of the board to the right of the reset button. It is labeled INT on the silk. If you cut the INT jumper, you can use this pin to connect the MCP2515 INT pin to a different IO pin.

Silent Mode Pin

• SLNT pin - located on the front of the board to the right of the reset button. It is labeled SLNT on the silk. This pin can be pulled high to put the TJA1051/3 transceiver into silent mode. From the datasheet:

In Silent mode, the transmitter is disabled, releasing the bus pins to recessive state. All other IC functions, including the receiver, continue to operate as in Normal mode. Silent mode can be used to prevent a faulty CAN controller from disrupting all network communications.