Thanks so much.
I have another question.
As mentioned at my question above, com1 of Plc#1 will be occupied by Xserver, so Auto485 must be connected to com1 of Plc#2. Then I-7022 will be connected to the second 485. Plc#1 will be master(sends or receives DM data of it to or from Plc#2). Now, all of com1s of Plc#1 and Plc#2 are occupied by Xserver and I-7022(via Auto485).
"Modbus Device" which mentioned at my diagram is the device of wireless SMS messages transfer (for sending commands to Plc, receiving alarms from Plc and sending the messages to operators). So to speak, it must act as another master on original 485 trunk line. As you mentioned at reply, only one master are allowed at single 485. If I connect the Modbus device to the original 485 line and talks with Plc#2, will be any communication problem?
Thanks and best regards,
BJ