Timing Diagrams

Does anyone know of a software package that will aid in creating timing diagram helpful in PLC programing. I have found that creating one for a system that is repeatitive, ie walking beam or index table, is very helpful while tring to be one with the system. I have drawn many on a napkin while catching a smoke out back. Have used AutoCad, good for electrical & mechanical drawing, tried Excel, ok if you can use some graphs. Also tried Circuit Timing Drigram software for memory chip and gates, too unque to its field but close.
My current project deals with an existing assembly machine with a PLS, programable limit switch, wired to SLC500 inputs. I am modifing the assembly machine to add some inspection stations. I have maintained and operated this machine, on & off, for the last year. So I have a good understanding of this machine, but everytime I go back to make a modification or debug a fault, I find myself relying on its timing diagram. Its the only thing that gives the big picture. Using this diagram convinces me that any cycil machine can be identified in term of degrees ( 0-360 )
Thus started my quest for a software package to aid in future designs and modification of other systems.

Any thoughts ?

P.S.I spent about 8 hour yesterday browsing thru the Q's & A's at this site, you guys are great. And I agree that the tangents are more educational then the direct answers. Unless you where looking for that answer.
P.S.S anyone want to get started on CTU/CTD AB style? This could be better than TON

My first comment is... You've got a PLC. Why bother with a PLS? Run the encoder directly to the PLC and eliminate the "middleman"...

As far as drawing timing diagrams... Perhaps you'll have better results searching for software designed to help generate cam profiles of mechanical cams. There's gotta be an add-on for AutoCAD that will spit out a timing diagram based on "fill-in-the-blank" parameters. You may even be able to find a free LISP program at one of the CAD site (like CADalog or CAD Depot), or try asking in the usenet CAD users groups

beerchug

-Eric