What exactly does this variable do? The manual states that it is "How the J1939 Frame is formatted for a DTC. There are four J1939 Versions from which to choose, and each has a unique bit format" However the SAEJ1939-73 standard states that the DTC frame format is
SPN: 19bits
FMI: 5bits
OC: 7bits
CM: 1bit

What value does this variable need to be at to use the standard format? Also, what are the other formats available?

Hello casher,

I'm so glad someone around is taking time to look through the reference manuals and specifications!

This is the SPN Conversion Method in the J1939-73, section 5.7.1.11.

Thanks for the question.