Page 1 of 1

Self made canbus board only working at 500kbs but not 1 Mbs

Posted: Wed Feb 20, 2019 6:14 am
by Markus1981
Good day everyone

I have designed a can bus board for my application which i based of the PICAN2 schematics .
The board is inteded to be used with a racecar ECU with a 1Mbs CAN bus

- My configuration is correct , when put the Pican on and configure to 1Mbs
==> Perfect communication
- I also modified a cheap module and replaced the Christal from 8 to 16 Mhz as well as modifiying the power for MCP2515 to a seperate 3.3V
https://www.dx.com/p/mcp2515-can-bus-mo ... GztWugzaMo
==> Perfect communication
- When i plug in my own designed Breakout board i receive nothing

When i change the configuration to 500 kbs and plug in my board into my OBD CAN BUS pins i get perfect communication

Therefore my conclusion its something to do with the board but not the settings .
I must add i tried with termination on and termination off but same result
Here is my Schematic:
https://github.com/BastianGschrey/Power ... apture.PNG

Can someone figure out why my board does not want to work at 1Mbs ?

Re: Self made canbus board only working at 500kbs but not 1 Mbs

Posted: Wed Feb 20, 2019 7:15 pm
by mark3112
I’ve not used the MCP2551 and normally use SN65HVD251 but guess the CAN interface is the same.
What are R1 & R2 for (the whole idea of CAN is that it is robust in noisy environments)? I would also lose R6 & R7 (at least during the testing phase).
The other thing that jumps out at me is the 2515 is fed from 3V3 but the 2551 is from 5V. OK maybe it should work but a level shifter wouldn’t hurt.

Re: Self made canbus board only working at 500kbs but not 1 Mbs

Posted: Wed Feb 20, 2019 7:28 pm
by mark3112
For a minimal CAN network take a look at Keil’s A Tiny Network without Transceiver ICs (bottom of page 4):

http://www.keil.com/download/files/canprimer_v2.pdf

Re: Self made canbus board only working at 500kbs but not 1 Mbs

Posted: Wed Mar 06, 2019 8:27 am
by Markus1981
Sorry for the late reply . I found my fault and it was a stupid one .
I connected R3 to Pin5 instead of Pin8 on the MCP2551 therefore the slope control was not connected .

Re: Self made canbus board only working at 500kbs but not 1 Mbs

Posted: Wed Mar 06, 2019 4:20 pm
by bertr2d2
Hi Markus,

please consider using a MCP2562 instead of MCP2551 (deprecated): http://lnxpps.de/rpie/

Regards

Gerd