When the program is complete, the last rung is the 'write to uv-prom instruction' which is mandatory for the CPU to go into RUN, The 'write to uv-prom instruction' is a straight line from the rail to a coil addressed 8176-16 (see below). When the program is loaded it will be saved and write protected. To make any alterations to the program, the uv-prom chips would have to be erased.
Note: The Sy/Max PLC line and software have been obsolete since 2015 and have been replaced with the M580. For more information and upgrade options contact your local Schneider sales office or distributor.