C.1 Diagnostic functions of PLC
PLC controller features additional functions that make locating errors easier. Errors can be divided into two categories according to severity :
1. Fatal errors are severe and they prevent PLC controller from operating until their cause is located and solved.
2. Non-fatal errors are those that do not prevent PLC controller from operating. After detecting one or more non-fatal errors, program execution will continue. Nevertheless, it is necessary to correct these errors as soon as possible.