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I discover a problem on my design, with a STM32F042K6 MCU and a MCP2561 Can Transceiver. I can send some frames on the CAN Bus but i can't receive any frames. When i put my scope probe on the CAN Rx Line between the MCU and the Transceiver o observe a bad low level voltage like this :

enter image description here

I have checked, this MCU Input is 5V tolerant.

What is the reason of this bad low level voltage ? I think it's why my MCU don't receive any acknowledge and any frames.

Is there a problem on the Transceiver or on the MCU ?

Thank's for your help !


It seems there is a problem on the ACK bit transmission : I don't understand why. Any idea ?

enter image description here

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  • \$\begingroup\$ It looks like a ground shift. Check if there are no parasitic resistances between Micro and Transceiver Grounds. Is it supplied from the same power source? \$\endgroup\$ – KJA Jun 20 at 8:16
  • \$\begingroup\$ It's power from two different regulators because the MCP2561 needs 5V and the MCU needs 3.3V. I checked the Tx Line and the levels are good (0V - 3.3V). It seems there is no resistances between MCU Ground and MCP2561 Ground. \$\endgroup\$ – VoltAd Jun 20 at 8:24
  • \$\begingroup\$ MCU ground and MCP2564 ground should be the same. As in, short circuit. Open circuit means this won't work properly. \$\endgroup\$ – Jeroen3 Jun 20 at 8:46
  • \$\begingroup\$ Yes, It's the same Ground !!! ;) \$\endgroup\$ – VoltAd Jun 20 at 8:55
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Ok, Thank's guys, i'm so sorry it was due to a bad solder on my MCP2561 Gnd Pin. On the TX Side, i'm facing a problem due to the ACK, i always encountered a timeout issue when i want to send a Can Frame : enter image description here

And the frame is received multiples times on the other CAN Equipment : When i send one frame, the MCU seems to send multiples frames until it reach the timeout.

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