I am having a problem with the transmit device on CANPort1 (J1939). I have 2 SPNs that I want transmitted. I have mapped these to the corresponding variables with the data. Both SPNs are in the same PGN.

When I look at the bus with the EControls CANCapture, I get the correct PGN, priority, and source address information on the bus, but there is no data. It is not FF, it is not 0, the whole data field is blank.

My work around has been to map the variables to a free form CAN message and use a state machine and timer to provide the cyclic rate.

Please check that the SPN definition is correct. The start byte and byte length may be incorrect. This information is used to calculate the DLC for the PGN. If this information is not correct, a 0 DLC may result. This would cause the PGN to be transmitted with no length.

If this is not the case, can you send a copy of the configuration?

The problem is that when an SPN is less that a whole byte it has issues. It is being tracked now in the Bugs section of the forum.