- Serial DF1: You can access serial MicroLogix PLC such the MicroLogix 1200 on the remote Digi Connect WAN's serial port. You either need to have an OPC server which can directly encapsulate DF1 protocols into TCP/IP or to use Digi RealPort to create redirected COM ports for RSLinx. Ideally, using the newer DF1 Radio Modem protocol can cut your data costs in half, but DF1 Full-Duplex or Half-Duplex can also be used. DH485 won't work via cellular due to the high latency. You must slow the PLC (ACK) timeout setting down to 30 seconds, so you cannot use a MicroLogix 1000 since it doesn't allow this parameter to be adjusted. DF1 Radio Modem has no DF1 (ACK) or (NAK), which is why it costs less to use.
- CSPv4 or AB/Ethernet: You can access legacy PLC such as SLC5/05 and PLC5E by enabling TCP port forwarding of port 2222 on the Digi Connect WAN. Under RSLinx you enter the IP or DNS name for your Digi Connect WAN in the "Ethernet Driver", then right click the driver to slow down the timeouts from default of 3 seconds to a cellular-friendly 30-seconds. For a bit of fun, open this link in your browser and you will access the web pages of my SLC5/05 through Cingular/GSM cellular - http://digiwan.gotdns.org:8080/. But please don't leave this page open since you'll impact other people trying to look at my cellular PLC.
- Ethernet/IP: You can access ControlLogix and other newer PLC supporting Ethernet/IP by enabling TCP port forwarding of port 44818 on the Digi Connect WAN. Under RSLinx you enter the IP or DNS name for your Digi Connect WAN in the "Remote Devices via Linx Gateway" Driver, then right click the driver to slow down the timeouts from default of 3 seconds to a cellular-friendly 30-seconds. You cannot use the RSLinx Ethernet/IP driver since it relies on UDP broadcast which cannot move across wide-area-networks.
If you want more detailed instructions, I have an application note online here: