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RACELOGIC Support Centre

What is CAN Send Acknowledge?

This option will cause the Video VBOX to make other active nodes on the connected CAN bus system aware that is it receiving messages. When connecting to an active CAN bus, this is normally not required, as the Video VBOX is simply listening for data.

Note: When CAN acknowledge is turned on, any mistakes in setup (for example incorrect baud rate set) may cause errors on the bus system. 

When is CAN acknowledge required?

CAN acknowledge is needed when connecting the Video VBOX to a CAN bus system which is not currently active.

For example, a direct connection to a sensor with a CAN interface. CAN acknowledge is used to start the transmission of information between the sensor and the Video VBOX. 

There are setups when this may be required when connecting to a vehicle bus system, for example, some vehicles CAN bus systems are protected by a CAN gateway interface. For successful data transmission, CAN acknowledge may be required to be turned on.  

So, how does send acknowledge work?

It is important to note that the ACK bit is part of a transmitted CAN frame and not a separate response frame.

If a device is configured to be active on a bus (i.e. acknowledge is enabled) then it will set this bit for every frame it receives. This assumes the device supports the version of the CAN frame (e.g. CAN 2.0 devices will not acknowledge CANFD frames).

The following image shows a single CAN frame being transmitted with no other active node on the bus.


The following image shows the same single frame being transmitted with at least one other active device on the bus. This time the ACK bit is set. In this case the bit is at a slightly different voltage because it is being driven by another device, not the one transmitting the frame.

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