You need to use the serial port on a SLC505 to talk to 3 devices. Two of them are ulogix over radio modems using DF1 protocol. The 3rd is a medina telemetry unit which supports DF1 point-to-point only. You would be able to use a 4102-MCM4-DFCM4 module. This module will support 4 ports of either Modbus or DF1 communications. Two of the ports of the module will be setup as a master to the two ulogix devices acting as DF1 slaves. The third port will then be either a full duplex master (polling data from the medina unit) or a full duplex slave (having the medina unit write data to our module). Even in full duplex mode, our module requires a master/slave relationship. The fourth and final port of the module would be used to provide all of the data obtained on the other 3 ports, back to the SLC processor DF1 port.