Please give the following info:
1) Is "Lg PLC" an abbreviation of "large", a model, or manufacturer?
2) What model and manufacturer are you dealing with? Every one of them handles clock functions a little differently.
3) Please post some speculation on your part about what a real time clock COULD be used for in a process control or manufacturing environment.
4) Please let us know how many entries the index in your text has on: real time clock, time functions, calendar, and clock functions.