CAN Bus Communications Decoded: What data is available?
What data is available?
|00:00||- In this next step, we're going to go through the list of required data that we've created in step 2 and determine which of the devices connected to the bus can provide the required data or if any other OEM devices in the vehicle are already providing it.|
|00:14||This is why it's often simultaneously done with step 2, it's essentially the inverse of that step.|
|00:20||Keep in mind however, there can be multiple sources for information.|
|00:25||An example of this could be a vehicle speed signal.|
|00:28||This might be able to be estimated by the ECU from engine RPM, current gear, diff ratio and tyre size information and then transmitted, or it could be transmitted directly from an ABS controller in terms of a wheel speed signal that could then be converted by the receiving device.|
|00:45||In this example, the second option is likely to be more accurate and it is the route that I would take.|
|00:52||Often the transmission profile of a device is fixed and it can't be changed.|
|00:56||This is usually not much of a problem as devices tend to transmit more data than is needed as long as the bus load isn't too high.|
|01:05||And there's no downside to there being extra data on the bus that isn't used.|
|01:09||An example of this would be the Link compound message format we discussed early in the complex CAN message module of the course.|