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CAN Bus Communications Decoded: Step 2: What Data Is Needed, and Where?

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Step 2: What Data Is Needed, and Where?


00:00 - So second step of the process is we need to know what data is needed and where, or like really tightly define that.
00:09 So if we just pop back over to my laptop again quickly, I've got the Link help file up here and just looking at the documentation for our Link CAN lambda modules.
00:20 Now couple of details around these particular modules in this vehicle.
00:25 They are currently configured as IDs 4, 5, 6 and 7.
00:32 So that means they're going to be transmitting data out on PIDs OX3BA to 3BD so if we were setting up the reception template, so that'd be something really critical that we'd need to know.
00:46 Coming down here we can see the packets that the CAN lambda devices can receive.
00:53 And this is the one that's going to be critical to us because this is where we're going to put our exhaust pressure signals through, the C125 is going to read those and then spit them out in this data frame here.
01:06 So just having a quick look at how this frame is going to be constructed.
01:10 We've got data bytes 0 and 1 here, so data 0 is just at 85 and that's going to be held constant.
01:18 Data 1 is not used so we're probably going to put a 0 there.
01:21 Data 2 is going to be the engine speed high byte and data 3 is going to be the engine speed low byte.
01:29 That's actually another nice feature that the Link CAN lambdas have is that they can control the operation of the heater elements in those wideband O2 sensors so that if the engine stalls, they won't keep the wideband O2 sensors sitting there heating up and possibly wearing out those elements over time.
01:45 So we are going to give it the engine speed data as well.
01:48 But to get the critical accurate readings that we need, it's the exhaust pressure measurement that we are more worried about at the moment.
01:56 So that is here, data bytes 4 and data bytes 5 and we've got absolute exhaust pressure high byte and low byte and this here we're just going to keep an eye on so times 10 and in units of kilo pascals or kPa.
02:11 So that times 10 multiplier and that unit is going to be really key.
02:16 We're going to have to make sure that those line up.
02:18 Data 6 here we want to set to greater than 1, greater than, it's actually greater than or equal to 1 if you read through the documentation a little bit further, it does mention that.
02:29 So we're going to set that to 1 to enable the back pressure compensation and then data 7 is going to be unused.

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