The specifications are for single board transfer systems with conveyors as the transporters. Specifications state that the boards should be moving from left to right although the same standard does apply to board transfers going right to left.
For proper sequencing of boards, one or two signal lines should be used; "Board Available" or "Machine Not Ready".
I think you need to get more specific information from your machine manufacturer, and if you post some more details (this is really hard-core "specific implementation," and not common knowledge), someone may be able to help.
Dick Grier. Author of Visual Basic Programmer's Guide to Serial Communications 4. See www.hardandsoftware.net.