CAN J1939 serial decoding

What it does

As with PicoScope 7 Automotive’s other Serial decoding tools, the CAN J1939 serial decoder converts CAN bus voltages to a human-readable form (typically hexadecimal but binary, decimal or ASCII formats are possible). However, the decoder is specifically built for decoding J1939 CAN protocol messages:

In addition to the CAN message parts that can be returned by a CAN serial decoder, the CAN J1939 serial decoder fully decodes the message identifier (ID) and splits it into its three constituent parts: the Priority, Parameter Group Number (PGN) and Source Address. When a suitable data-to-text file, relating the ID values to their descriptions, is supplied and selected, full-text descriptions of the PGN and Source Address are displayed in the decoding table.

How it can help you

The PGN and Source Address values within a CAN J1939 message ID can provide valuable diagnostic information:

The PGN gives you a reference to the SAE J1939 standard’s Suspect Parameter Numbers (SPNs), where you can look up how to locate and scale/offset the data in the message payload. This is particularly useful if you need to check whether the data is valid but have no other way to access it.

Diagnostically speaking, the Source Address can be even more useful: By using the global Source Address ID list in the SAE J1939-DA document to create a data-to-text description file and then selecting it in the decoder, the decoding table can display the descriptions of all the CAN controllers communicating on a network. This can tell you exactly which controllers are online, offline or might be causing network issues.

How to use it

Open and follow the J1939 serial decoding Guided test in PicoScope 7 Automotive to decode the messages on machines or vehicles that use the J1939 protocol.

Alternatively, if you have prior experience with the Serial decoding tools, you can manually set up a CAN J1939 serial decoder by opening the More… panel and clicking the Serial decoding icon. Then select the CAN J1939 decoder and click Next to proceed with the rest of the configuration steps, as demonstrated below.