Change J1939 Transmit Speeds By Math Channel

Carl 5 years ago in IQANdesign updated by Gustav Widén (System support) 5 years ago 2

Hi Guys,

Since in J1939, Transmits speeds of CAN messages can very, i.e. 1 second transmit rate, changing to 100ms on function, at present, only a set figure can be put in to the transmission speed.

If this could also be available to look at a math channel, then thing like DUELs could be used to change the speed.


If you want to dynamically change the transmit rate, what you can do is define an IDC as your message trigger and make it oscillate at the desired rate.  Then set your JFOUT channel to "on trigger" with transmit rate set to "not used" with the trigger being your IDC channel.

The on trigger method is probably the best choice as long as the application cycle time is faster than the transmit rate. 

If the cycle time is equal to the fastest transmit rate needed for the JFOUT, then there is another workaround that is less elegant: Duplicate the JFOUT:s and JPOUT:s in separate function groups, give the JFOUT:s different transmit rates, and only enable the FG that has the transmit rate that is currently needed.

A small drawback of creating a variable transmit rate is that only fixed transmit rates work with the 5.00 feature that even out CAN bus utilization.