TCAN1042HV: abnormal signal at last bit

Victor Chen_HK

Part Number: TCAN1042HV

Hi,

Abnormal signal was obtained during the evaluation of TCAN1042HV. This issue always happened when there are more than 2 nodes.

No issue when it is point to point communication(2 nodes).

screen cap and schematic as following. Customer only implemented the termination resistor at 1 node.

Thanks,

Victor

over 7 years ago

0 Michael Peffers over 7 years ago

TI__Mastermind 20820 points

Hi Victor,

This is normal in CAN, it is the ACK bit that all nodes transmit after successfully receiving a CAN frame.

Mike

0 Victor Chen_HK over 7 years ago in reply to Michael Peffers

TI__Expert 5130 points

Hi Mike,

Thanks for your quick response.
Do you mean that the ACK bit should be seen when there are only 2 nodes as well?

Best regards,
Victor

0 Michael Peffers over 7 years ago in reply to Victor Chen_HK

TI__Mastermind 20820 points

Hi VIctor,

Whenever a CAN controller (MCU) sees a valid CAN/CANFD packet it is going to send an ACK to the bus. Here is an example of the classic CAN packet structure:

So, once a controller see a valid frame it send the ACK bit. The ACK bit then causes the voltage on that bit to be outside of the typical CAN levels due to multiple nodes driving dominant at once. This only occurs when there are more than two nodes as the transmitter will not ACK itself. Please let me know if you have anymore questions?

0 Victor Chen_HK over 7 years ago in reply to Michael Peffers

TI__Expert 5130 points

Hi Mike,

Thanks for the details.

Do you mind uploading the picture again? It is not showing correctly.

Thanks,

Victor

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TCAN1042HV: abnormal signal at last bit