Ready to perform a CAN Bus acquisition but don’t have a .dbc file immediately available to decode the data? No problem!
In Simcenter Testlab and Simcenter Testlab Neo, it is possible to record the raw CAN Bus data stream and decode it later in a offline mode. A CAN bus settings *.dbc file is needed for the decoding, but the file is not needed to record the raw CAN Bus stream. The *.dbc file can be used to decode the raw CAN signals in post processing.
This article has the following contents: 1. Simcenter Testlab: Offline CAN Bus Recording 2. Simcenter Testlab: Decode Raw CAN Offline 3. Simcenter Testlab Neo: Decode Raw CAN Offline 4. OBDII Versus CAN Bus Decoding
To record the raw CAN stream in Simcenter Testlab, open Simcenter Testlab Signature. In the Channel Setup workbook, choose the “CAN Settings” view from the dropdown in the upper right as shown in Figure 1.
Figure 1: Go to the “CAN Settings” view.
Setup the raw acquisition as shown in Figure 2. Note this is available in Version 16A and higher:
A: Select the Can Device used for the acquisition. B: Enter a baud rate, for most vehicles this is 500000 C: Set the device to “Passive” D: Click “Apply” to apply the settings. E: Go back to the standard “Channel Setup” view.
Figure 2: The “CAN Settings” workbook.
Back in the standard “Channel Setup” view, you will notice a new pane: “Digital Bus Channels” in the lower left of the screen as shown in Figure 3.
Figure 3: The “Digital Bus Channels” pane appears in the Channel Setup workbook.
In this area, there is an option to “Save Raw Data”. Check on this option. The raw CAN stream will be acquired.
NOTE: Most SCADAS hardware is able to record raw CAN data for later decoding. However, Vector boxes will not support the recording of raw CAN streams. Vector boxes were primarily used with the Scadas III hardware before CAN was embedded in the XSI of the SCADAS Mobile / Recorder units, or the SYSCON, the CN4 card, or the SCADAS XS. Measuring OBDII channels is also not supported with Vector boxes.
2. Simcenter Testlab: Decode Raw CAN Offline
In the "Navigator" worksheet of Simcenter Testlab, place the entire run into the Input Basket (replacing just the LDSF or RDDF is not sufficient). Right click on the run name and choose “Replace in Input Basket” as shown in Figure 4.
Figure 4: Replace the entire run in the Input Basket.
NOTE: The LDSF contains the raw time data from the run. The RDDF contains the raw CAN Bus stream. The RDDF and LDSF are separate files, though they are stored in the same directory as shown in Figure 5.
Figure 5: The raw CAN stream will be stored in an XSI-CAN file like the one shown above.
NOTE: If there is no RDDF called “Digital Bus Data” it means the raw CAN Bus was not recorded.
In the Time Data Selection workbook (see Figure 6):
A: Ensure the “Data Source” is set to “Input Basket”. Click “Replace” to import data. B: Click the “Import digital bus channels” button (black arrow and two yellow lines). C: Select the .dbc file corresponding to the CAN device. D: It is recommended to change “Interpolation” from “Sample and Hold” to “Linear”. E: Click “OK”. F: New channels are created for all decoded CAN signals. G: Save the decoded CAN Bus channels into the project by pressing the “Save As…” button. The data will be stored in the project and can be viewed in the Navigator workbook.
Figure 6: Create new channels for all decoded CAN signals.
The decoded CAN Bus data is saved into the throughput file of a new folder in the Navigator workbook as shown in Figure 7.
Figure 7: The data is saved into the Throughput folder.
Note that this feature is supported on the built-in CAN Bus interface on Simcenter SCADAS Mobile, Simcenter SCADAS Lab, and Simcenter SCADAS XS.
Figure 8: CANBUS interface on SCADAS Mobile
Recording raw CAN Bus is not available with the USB based Vector box used with SCADAS3.
3. Simcenter Testlab Neo: Decode Raw CAN Offline
To decode raw CAN Bus data in Simcenter Testlab Neo, right click on the throughput file folder and select "Extract Digital Bus data" as shown in Figure 9.
Figure 9: Decoding raw CAN bus data offline in Simcenter Testlab Neo.
This can be done in the Desktop of Simcenter Testlab Neo. Provide the DBC file when prompted.
4. OBDII Versus CAN Bus Decoding
Legislated OBDII signals and CAN Bus signals should not be confused with each other, they are separate signals. For emissions testing, some signals (like engine rpm, vehicle speed) are made available on the OBDII (Onboard Diagnositic) post of many vehicles, which is also used to record CAN Bus signals.
Legislated OBDII signals do not get recorded in the raw can stream. They must be actively requested during acquisition. They are not broadcast on the CAN Bus by default.
