CAN Bus Configuration
There are four different CAN bus configuration tasks that can be performed in this window:
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Set the bit rate for the CAN bus. |
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Enable or disable CAN bus termination. |
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Define signals (measurements) that should be sent to devices on the CAN bus. |
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Identify each type of message that may be received from the CAN bus. |
To open this window, select ECU > CAN Config in the menu bar.
Setting the CAN Bus Bit Rate
The Bitrate dropdown at the top of the top of the window is used to set the bitrate of the CAN bus. All devices on the bus must use the same bitrate.
CAN Bus Termination
A CAN bus must have exactly two termination resistors, one at each end. If you wish to use the ECU as one of the endpoints:
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Check the Enable CAN Termination box. |
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Ensure that there is one (and only one) other termination resistor on the bus. |
If you already have two termination resistors on the CAN bus, uncheck the Enable CAN Termination box. This allows the ECU to act as a node in the middle of the network.
Sending Data to Devices on the CAN Bus
It's possible to send any ECU measurement to any other device on the CAN bus. Follow these steps for each parameter that needs to be transmitted:
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Click the Add button in the CAN Messages group. The Add CAN Message window appears. |
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Fill out the fields in this window as follows: |
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ID (hex): The numerical ID of the message. This must be unique on the CAN network and also represents message priority (lower numbers are higher priority). |
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Name: A descriptive name for the message. |
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Length: The number of bytes in this message. |
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Frequency: The number of times per second that this message should be sent. |
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Type: For sent messages, this should be set to Output. |
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The new message will now be listed in the CAN Messages group. Select the new message in the list (click on it). |
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Add the measurements that will be sent in this message. For each measurement to be added: |
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Click Add in the Measurements group. A list of available measurements appears. |
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Double click on the measurement you want to add. The selected measurement will now appear in the Measurements List. |
Receiving Messages From the CAN Bus
Messages from the CAN bus can be mapped to any one of a number of predefined inputs. Follow these steps:
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Click the Add button in the CAN Messages group. The Add CAN Message window appears. |
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Fill out the fields in this window as follows: |
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ID (hex): The numerical ID of the message. This must be unique on the CAN network and also represents message priority (lower numbers are higher priority). |
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Name: A descriptive name for the message. |
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Length: The number of bytes in this message. |
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Frequency: The number of times per second that this message should be sent. |
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Type: For received messages, this should be set to Input. |
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The new message will now be listed in the CAN Messages group. Select the new message in the list (click on it). |
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Specify the inputs to which this message will be mapped. For each input to map: |
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Click Add in the Measurements group. A list of available inputs appears. |
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Double click on the input you wish to use. The selected input will now appear in the Measurements List. |
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Configure the format of this data for this input. See Measurement Format, below. |
Measurement Format
There are a number of settings that format each item in the Measurements list.
As you configure these settings, you can see the bit format you are configuring in the lower left corner of the window.
The blue and orange bits represent the row you have selected in the measurement list on the right side of the window.
If bits are red, it means there is some problem with the configuration. For example, if you indicate that your first measurement takes up 11 bits, but your second measurement starts on bit 8, the data would overlap.
Start Bit
The bit of the message that this measurement starts on. For example, if the first measurement in the message starts on bit 0 and is 8 bits wide, it will take up bits 0 to 7. So, the second measurement would likely start on bit 8.
Width
The number of bits used to encode the value of this measurement.
Byte Order
Indicates whether the most significant bit is the first bit or the last bit of this measurement.
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Intel. The most significant bit is stored last (little endian). This is typically the case with Intel processors. |
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Motorola. This most significant bit is stored first (big endian). This is typically the case with Motorola processors. |
Type
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Signed. The value indicates whether it is positive or negative. |
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Unsigned. The value contains only positive numbers. |
Gain and OFFSET
CAN messages use these values to optimize the way data is encoded.
When sending a message (output messages), the value actually encoded for the measurement is equal to:
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(Measurement - Offset) / Gain |
When receiving messages (input messages), the value to be used is calculated by applying the following formula to the received value:
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(Received value * Gain) + Offset |
Min
The minimum allowed value for this parameter.
NOTE: Clicking Calculate Min and Max tells VCM Live calculate these values automatically based on the other configuration in this row
Max
The maximum allowed value for this parameter.
