If you want to prevent hacking from the Internet (since you mentioned router) then you should use i-TRiLOGI "Controller->Ethernet & ADC Configuration" screen to create a password and check the "Use username/password" radio button to "Yes". This password will prevent unauthorized access from the Internet via i-TRiLOGI or the web browser, but will not affect serial device (such as FP4030MR) that has physical connection to the PLC.
The SETPASSWORD keyword is actually a legacy feature in the PLC that is seldom used today. In 1993 when our T100MD and T100MX PLCs were first designed for OEM, the term "Internet" did not even exist (there were networks such as Bit-net used between universities, but nothing for the public) . Back then the only way to connect to a remote PLC was to use two telephone lines connected via dial-up modem, one on the PC side and the other on the PLC side. The modems typically ran at 1200, 2400 or up a zippy 9600 bps(!). Since the modem is connected to a telephone land-line anyone who knows the phone number can dial in and control the PLC using the TRiLOGI software. The SETPASSWORD command was created to prevent unauthorized access by demanding the connecting software presents the unlock password before any further communication is possible.
We still support the SETPASSWORD feature for backward compatibility but it is not really needed today since landline modems can now only be found in the same museum along side the dinosaurs
