When I am programming and I install the XIC function does the PLC perform this function on every scan or just on download of program?The same question for the SUS function?

Guy, when you are progamming and install a XIC function in PLC, do you need download a program. If do you using CLP's Rockwell this process is very easy

Normaly in every scan,

In Logix5000, the main task is, by default, continuous. You may have only one continuous task in the program. All of the code within the continuous task is read every scan, unless you have specific jumps or other program control elements designed to jump past it or only scan it on certain conditions. Any other tasks you add to the program will operate on some kind of interrupt basis – hardware or timed. The former is only scanned if the hardware condition is met and timed interrupt operate at regular timed intervals that you can configure. They are called interrupts because they interrupt the main background scan. The correct use of all of these facilities is much too big a subject to discuss in a post like this.