When in logix 500, go to tools and select compare.
select the main program and compare program.
I select all in the next pop up window.
when the compare appears, select the ladder program, timer, counter file to compare.
In the upper left of the comparison window, select only changed rungs if its a program file or only changed data if its a b3,t4, c5 type of file.
it's much faster.
I don't know of any other way to do a comparison, maybe someone else will know of another way.
james