Overload and error differentiation by a CAN controller

Question

How does a CAN controller differentiate the overload frame and error frame when it was received on the CAN bus?

As far as I know, theses two frames are having the same frame format. In my project, I mostly encountered an error frame rather than an overload frame.

Answer 1

I found this:

"The Overload Frame is identical to an Active Error Frame. The only difference is that an Overload Frame does not increase the error counters (see error confinement) and does not causes a retransmission of a frame. Every node may transmit consecutively only 2 Overload Frames."

In: http://www.softing.com/home/en/industrial-automation/products/can-bus/more-can-bus/error-handling/overload-frame.php?navanchor=3010518

Answer 2

You are right: overload frames and error frames look the same. However, a CAN node can distinguish them by the time when the frame was received: An overload frame will only occur during the interframe space, and an error frame only during an actual CAN frame. Source.

Answer 3

Both an error frame and overload frame has the same format in case the node is in error active mode. But how can the CAN controller differentiate both is based on the position of occurrence in the CAN frame.

An error frame will be transmitted whenever a node detects an error whereas an overload frame is transmitted only in IFS (inter frame space).