CAN-FD hardware

dc42

We use the MCP2542 chips for driving the CAN bus. They have a separate power pin for the MCU interface, so they can level shift between a 3.3V MCU and still use 5V to drive the CAN bus.

Kulitorum

What is the max cable length for the CAN-FD Bus?

Kulitorum

JoergS5

@dc42 Thank you. I hope the MCP25 family is compatible with each other. If not, I will let you know...

JoergS5

@Kulitorum According to the table in https://www.computer-solutions.co.uk/info/Embedded_tutorials/can_tutorial.htm it is 10 m (ISO 11898-2 2015). Small house

dc42

Max cable length depends on the data rate and the number of devices on the bus. We use 1Mbits/sec as the base data rate. Page 5 of http://www.ti.com/lit/an/slla270/slla270.pdf suggests 1Mbits/sec should be OK to 40m length. The fast data rate will be configurable, https://duet3d.dozuki.com/Wiki/Gcode#Section_M952_Set_CAN_FD_bus_data_rate.

T3P3Tony

@Kulitorum 40m.. slighly larger house

Kulitorum

I was hoping for 150m

Will everything work at 0.25Mbps?

Kulitorum

dc42

Currently it would need a new firmware build to change the base data rate, because everything (including the bootloaders on the expansion boards) needs to know what that data rate is. Using lower speeds might work if the machine isn't tool complex and doesn't print sequences of tiny segments fast, so that we don't need to send movement commands to expansion boards at too great a rate.

Kulitorum

hehe, shame.

I print 1000mm/sec with vertices for every 5mm...

So can I amplify the signal every 40 meters? - Do expansion boards daisy chain?

JoergS5

I saw there exist CAN-FD repeaters, maybe an option.

It exists a CAN FD repeater reference design by http://www.ti.com/lit/ug/tidudb5a/tidudb5a.pdf (for an optional extension card maybe).

T3P3Tony

@Kulitorum said in CAN-FD hardware:

Do expansion boards daisy chain?

yes, but only physically, they don't amplify/act as an active repeater.

Kulitorum

@JoergS5 Thanks, looks good.

Kulitorum

Once I receive the expansion boards, I will experiment with this. Any ETA?

T3P3Tony

@Kulitorum will be emailing those who expressed an interest in the prototype boards after TCT show next week (you are on the list!)