Hi letranlong,
You have not told what software you are using.
For GX-Developer if you want to password protect the PLC se attached.
You have to be online on the PLC to do it.
I do not fond to use password on PLC's. If it really is necessary, then use it on FC's og FB's.
That can be done with the GX IEC og the Works software.
/Dariusch