Hi ebabtain,
Your instincts are correct. The ExcelReadWrite Add-In only reads in each worksheet once. This is by design, since the steps are generally executed many times and very quickly, and re-reading the file would consume a great deal of time.
Within the ExcelReadWrite Add-In there is a worksheet cache of sheets (called _sheets) that is checked against and does not bother to read the file if the worksheet if it is already cached.
So, I would suggest a few possibilities:
1. Modify the Add-In to remove the caching. or
2. Use another Add-In (such as text file read-write... this has less overhead)
In either case, make sure your logic in the simulation does not call the step more than - say - once a second.
Let me know if you have more questions and/or if I am missing the mark.
Cheers,
Dan