# Raspberry Pi CM4 HAT
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The board is designed for connecting CAN bus to Raspberry Pi. It gives access to Cyphal (opens new window)/DroneCAN (opens new window) (old name UAVCAN)
# 1. General
# 1.1. Variations
There are two connection options.
| RPI CM4 | RPI4 Common |
|---|---|
 |  |
# 1.2. Main function
# 2. Hardware specification
# 2.1. Features
- CAN to RPI-SPI - MCP2515-I/ST
- FDCAN to RPI_SPI - MCP2517FD-H/SL
- FT1 - RPI_SDCARD
# 2.2. Wire
Connectors
| № | Name | Description |
|---|---|---|
| 1 | CAN1, CAN2 | First CAN port |
| 2 | CAN3, CAN4 | Second CAN port |
| 3 | SWD | Serial wire debug from RPI to STM |
| 4 | DEBUG | SWD |
| 5 | STM-USB | |
| 6 | XT30PW-M | Power input |
| 7 | IR1 | InfraRed UART RX/TX |
| 8 | SERIAL1 | RPI ttyS0 |
| 9 | J8,J9 | Bottom connector slot |
| 10 | RPI1 | RPI4 header |
| 11 | J1,J2 | Compute Module 4 headers |
| 12 | RPI-USB | RPI USB Type-C |
| 13 | FT1 | SD CARD to extend memory of RPI |
| 14 | J5 | Ethernet RJ45 connected to RPI |
Pin configuration and functions
Pin configuration for RPI
| GPIO | Defedition |
|---|---|
| GPIO25 | SWCLK |
| GPIO24 | SWDIO |
| GPIO18 | Green led |
| GPIO15 | PI_RXI - STM_TX |
| GPIO14 | PI_TXO - STM_RX |
| GPIO10 | MCP2515_MOSI |
| GPIO9 | MCP2515_MISO |
| GPIO11 | MCP2515_SCK |
| GPIO8 | MCP2515_nCS |
| GPIO7 | MCP2515_nCS |
RPI UART map (opens new window)
| TXD | RXD | CTS | RTS | Board | Pins | ||
|---|---|---|---|---|---|---|---|
| uart0 | 14 | 15 | 8 | 10 | |||
| uart1 | 14 | 15 | 8 | 10 | |||
| uart2 | 0 | 1 | 2 | 3 | 27 | 28 | (I2C) |
| uart3 | 4 | 5 | 6 | 7 | 7 | 29 | |
| uart4 | 8 | 9 | 10 | 11 | 24 | 21 | (SPI0) |
| uart5 | 12 | 13 | 14 | 15 | 32 | 33 | (gpio-fan) |
# 2.3. Specifications
Mechanical
| Width, mm | Length, mm | Height, mm | |
|---|---|---|---|
| Outline | |||
| PCB |
Total weight of device is 6.6 g.
You can download 3D model on GrabCAD (opens new window)
Housing
Information about case presented here.
Absolute Maximum Ratings
| Parameter | MIN | MAX | UNIT |
|---|---|---|---|
| Vin (CAN1) | 5.5 | 55* | V |
| V (CAN2, CAN3) | 4.5 | 5.5 | V |
| I max | A | ||
| Operating temperature |
*Noted Voltage should be delivered only with current limitation under 2.5 Amp.
Recommended operating conditions
| Parameter | Value | UNIT |
|---|---|---|
| Vin (CAN3) | 30 | V |
| V (CAN1, CAN2) | 5 | V |
| I max | A |
ESD ratings
| Description | Value | UNIT |
|---|---|---|
| Human-body model (HBM) | 2000 | V |
| Charged-device model (CDM) | 500 | V |
# 2.4. Description
Functional Block Diagram
Connection example diagram
# 2.5. Power Supply Recommendations
Device is designed to operate from an input voltage supply range between 4.5 V and 5.5 V over CAN2 or CAN3 connector, or 5.5 - 30 V from CAN1. This input supply must be able to withstand the maximum input current and maintain a stable voltage. The resistance of the input supply rail should be low enough that an input current transient does not cause a high enough drop that can cause a false UVLO fault triggering and system reset. The amount of bulk capacitance is not critical, but a 47-μF or 100-μF electrolytic capacitor is a typical choice.
# 2. Led indication
- LED1
- PI_LED_nPWR - RED
- GPIO18 - GREEN
- PI_nLED_Activity - BLUE
# Useful links:
- cm4io datasheet (opens new window)
- cm4 datasheet (opens new window)
- waveshare.com/cm4-nano-a.htm (opens new window)
- raspberrypi.stackexchange.com/questions/104464/where-are-the-uarts-on-the-raspberry-pi-4 (opens new window)
# Useful links about RPI:
# Inspired by
- waveshare.com/rs485-can-hat.htm (opens new window)
- waveshare.com/wiki/RS485_CAN_HAT (opens new window)
- waveshare.com/wiki/File:RS485_CAN_HAT_Schematic.pdf (opens new window)
# 2.6. Revision history
| version | Description |
|---|---|
| v |