Solution:

The jumper in the FOSTCDR is for a level triggered 485 enable instead of an edge trigger. All it allows you to do is to pass a break condition. If the protocol does not need a break, you should never have to set the jumper. I think it would be more confusing than enlightening to include a description in the data sheet. It was included mainly for custom modifications that require the break setting. I don't think the jumper pins are even being stuffed. - KN The JP1A jumper permits a custom version of the FOSTCDR to support break. - twr