CAN channels use Vector CAN databases or eDAQ CAN databases to decode specific signal values from incoming CAN messages on
NOTE
The eDAQ CAN databases are currently supported only by the CX23-R/eDAQXR CAN interface. They are not currently supported by the MX471B-R or MX840B-R CAN interfaces.
The MX471B-R and MX840B-R support up to 128 database channels for each CAN connector. There is no limit on the number of database channels for unit CAN connectors. The unit also supports active queries (SAE® J1939-21 PGN requests) on up to 75 database messages per CAN connector.
For each signal, a CAN database file specifies which CAN message ID (or IDs) carry the signal, the bit position and length of the signal within the CAN message payload and the format of the signal data, including its endianness, scaling and offset. When a database has been imported into a unit, this information about each signal is displayed in the Databases page accessible in the System view.
In some cases, a signal may be carried in more than one CAN message ID. For example, SAE J1939 designates 8 of the CAN message ID bits as a "source address." SAE J1939 CAN messages transmitted by different source nodes in a CAN network may have different message IDs while still referring to the same SAE J1939 PGN and carrying the same signal. To accommodate such situations, a unit CAN database can specify both a CAN message ID value and an optional bit mask. To decide whether an incoming CAN message carries a particular signal, the bitwise-AND of its ID with the database bit mask is compared to the bitwise-AND of the database message ID value with the bit mask. If a mask is not specified, the message IDs must match exactly.
The eDAQ text database file format allows the user to explicitly specify both the message ID value and the bit mask. When imported into a unit, these values are shown in the Databases view as the "Value" and "Mask," respectively.
The Vector DBC database file format contains information about each message and signal which the unit uses to automatically determine an appropriate bit mask. SAE J1939 messages with a "null" source address value (0xFE) cause the unit to generate a mask which ignores the source address portion of the CAN message ID. SAE J1939 messages with a specific source address value and all non-J1939 messages, cause the unit to omit the mask, so that the specified message ID must be matched exactly. The message ID value and mask determined by the unit are shown in the Databases view as the "Message ID" and "Mask," respectively. The Mask value will be blank if masking is not being used (that is, if the CAN message IDs must match exactly).