Need to save workbook on cell changed by hot link.

I am working on a project where a spreadsheet gets data from a PLC via RSLinx OPC. Any way that part works, and I have a macro that will save the workbook
with a name from a cell, but i need to trigger the macro by changing a certain cell.

This should be easy for somebody. Not me.

I can write from the PLC to any cell. The problem is that change() doesn't work unless the change is entered from the sheet and not by the link.

calculate() could work, but I don't know how to make it look at only one cell. do You??