When a personal computer (GX Works2) is connected to the RS-232C port of a programmable controller, communications between the personal computer and the programmable controller may be disabled depending on the communication settings for the RS-232C communication equipment.

Connect the personal computer to the built-in programming port of a programmable controller CPU module and change the communication settings so that the communications between the personal computer and the programmable controller can be established. (Types of the connecters, such as RS-422 and USB, to connect to peripherals differ depending on the series.)
To read and write a program through the RS-232C port using a programming tool, such as GX Works2, the communication setting values need to be cleared to 0. (The register value of the communication is 0.)

When using GX Works2, click the "PLC System(2)" tab and deselect the "Operate Communication Setting" checkbox.

Reference) Multiple connection destinations can be set in GX Works2.
　　　 To set multiple connection destinations, create data for each connection destination on the "New Data" window.
　　　 For details, refer to the following.
Section 14.1 in the GX Works2 Version 1 Operating Manual (Common) (Manual number: SH-080779ENG)