In Version 3 of the SB-Assembler this directive will perform a boundary sync.
The label field of the source line containing the .EM directive should be empty.
It is not possible to define a label on the same line.
Everything on the source line following the .EM directive will be ignored.
In Version 3 the user is warned in pass 2 if an orphaned .EM directive is found. An orphaned .EM is one which does not have matching .MA directive.