Solution:

It depends on which type of PLC you use. In other words, you should check terminating character of your PLC's command first. If PCLS-920 doesn't support this terminating character, I think there is no way to do that. If terminating character is provided by PCLS-920, you can use RS-232 block which is located in TASK toolbar to try to connect PLC. When you double click RS-232 block, you'd better adjust idle and wait time to fit the timing of PLC. The following is the terminating character PCLS-920 provides: ,,,,,,NONE.