Solution:

After activate the RTS control of ADAM-4530, such application should be no problem. Basically, this module just designed for Leased Modem. You can use them in "Non-addressable" mode, besides, those two Leased Modems should be setting to "Dial" and "Auto Answer". For example, I/O Unit/PLC/ADAM-Network - (Connected to) - ADAM-4530 - (Connected to) - Standard MODEM - (Connected to) - (0-20Km of leased 2 or 4 wire MODEM Connection line) - (Connected to) - Standard MODEM #2 - (Connected to) - ADAM-4530 - (Connected to) - I/O Unit/PLC/ADAM-Network #2