Information on DBC-file support

This page describes the DBC-parser used by the decoders. The DBC-parser supports a subset of the DBC-file keywords, necessary for decoding of data.

Keywords

The DBC-parser supports the following keywords.

Keyword	Description
`BO_`	Message definition
`SG_`	Signal definition
`BA_`	Attribute value
`BA_DEF_`	Attribute definition
`BA_DEF_DEF_`	Attribute default value
`SG_MUL_VAL_`	Extended multiplexing definition
`SIG_VALTYPE_`	Extended value type definition

Note

Unsupported keywords can be removed from a DBC-file to reduce parsing-time.

Attributes

The DBC-parser supports a range of custom attributes.

ID-format

The message ID-format is specified using the DBC-file attributes BusType (string) and ProtocolType (string) as defined below.

ID-format	`BusType`	`ProtocolType`
LIN	`LIN`
CAN	`CAN` / `CAN FD`
PGN	`CAN` / `CAN FD`	`J1939`

Note

If BusType is not defined or empty, the parser assumes that the ID-format is CAN.

Note

When ID-format PGN all extended-ID messages are interpreted as PGNs. The commonly used attribute VFrameFormat is not used.

For examples see BusType / ProtocolType attribute examples.

Transport protocol

Some bus networks use one or more transport-protocols for transporting payloads (data bytes) exceeding the capacity of a single bus frame. For more information see Information on transport protocol support.

The DBC-parser supports a custom attribute TransportProtocolType used to specify if a message uses a transport protocol as defined below.

Transport protocol	`ProtocolType`	`TransportProtocolType`
J1939-21	`J1939`
ISO-15765-2 / ISO-TP		`ISOTP`
IEC 61162-3 / NMEA-2000 (fast packet)		`NMEATP`
CSS MUX-TP		`MUXTP#<S1>:<S2>:<S3>:<S4>`

The MUXTP transport protocol type takes additional arguments (<S1>:<S2>:<S3>:<S4>) to map muxed channel indexes to new virtual channel numbers (decimal values).

Note

If ProtocolType is set to J1939, the static J1939-21 transport PGNs (EB00 and EC00) are automatically assumed to be transport-protocol messages.

For examples see TransportProtocolType attribute examples.

Message ignore

The DBC-parser supports a custom attribute MessageIgnore used to ignore certain messages defined in the DBC-file. This can be useful to ignore message without removing them completely from the DBC-file.

The MessageIgnore is a message-level attribute (specified by BO_) and takes the following values (INT):

MessageIgnore = 0: Message is included
MessageIgnore = 1: Message is ignored

The default value can be used to specify if messages should generally be either included or ignored - if no specific value is provided.

For examples see MessageIgnore attribute examples.

Signal ignore

The DBC-parser supports a custom attribute SignalIgnore used to ignore certain signals defined in the DBC-file. This can be useful to ignore superfluous signals, such as e.g. multiplexor switch values.

For examples see SignalIgnore attribute examples.

Signal encoding

The DBC-parser supports the signal encodings defined below.

	Supported	Unsupported
Endianness	Intel, Motorola
Signedness[1]	Unsigned, Signed
Extended value types	32-bit IEEE-float[2], 64-bit IEEE-double[3]

Note

Invalid / unsupported signals are ignored as if not present in the DBC-file and parsing continues

Multiplexing

The DBC-parser supports both standard and extended-multiplexing.

When using extended-multiplexing, the parser supports the following switch formats:

Switch	Supported	Example
Single	-	`1`
Range	+	`1-1` or `1-10`
List	-	`1;3;5-10`

Note

A single switch value can be constructed using range with from and to set to the same value.