How to add CAN-FD to an SKR Pro v1.1 and v1.2 and connect a CAN-FD Toolboard


From 3.5b2, it is now possible to use one or two toolboards with an STM32F4 based board using the CAN-FD protocol. To do so, you must purchase a separate SPI to CAN-FD module. TeamGloomy have worked with Flymaker/Mellow to produce 3 designs of module to suit the board you are using.

For the SKR Pro v1.1 and v1.2 we recommend the driver module, which can be purchased from Aliexpress.

Connecting the driver module

You need either a spare driver slot or you replace an extruder driver with a toolboard. The driver slot should ideally be the last one on the board and have a working voltage of roughly 24v.
The driver slot you are going to use should be put in SPI mode. This is done using jumpers as shown below.

SKR Pro v1.1 and v1.2 SPI Jumpers

Install the driver module. Ensure module is installed so the hole thats in the same position as the diag pin is closest to the driver socket.

Driver SPI to CAN-FD Module
Driver SPI to CAN-FD Module

Wiring for the driver module

CAN-FD only requires 2 wires to be connected between each board, CAN-H and CAN-L.
We recommend using stranded twisted wire pairs, such as those found in ethernet patch cables.

Using the image below, the H connection is the CAN-H connection and should be connected to CAN-H on the toolboard. L is the CAN-L connection and should be connected to CAN-L. The two R connections are for the 120 ohm resistor and should be connected together.

Driver SPI to CAN-FD Module Connections
Driver SPI to CAN-FD Module Connections

Board.txt changes

The following two lines should be added to board.txt and assume the last driver slot is used. If another driver slot is used the appropriate CS pin must be chosen.

//CAN-FD Interface
can.csPin = PD_6
can.spiChannel = 2

Don’t forget to reduce the number of smart drivers if you are replacing a driver with the drive SPI to CAN-FD module.

Config.g Changes

If successful, the toolboard should show in the object model.
See this page for more information about CAN addresses etc.