Powerflex drives (at least the ones I am familiar with) use a protocol called "DSI". It stands for Drive Serial Interface and is an Allen Bradley protocol. Of course a lot of this varies based on what PLC you are using, and I'm delving into the subject myself, but you need to remember a few things about cables:
1. A cable is more than just "a connection". Even if a cable has the appropriate connectors the pins may or may not be correct, and this goes for voltages too. Some PLCs have an RJ-45 port (such as my SLC 5/03), but one of the wires runs at 24V, which will fry a standard nic used in computer ethernet applications.
2. You need to familiarize yourself with RSLogix and the different cable types for connecting, if you have specific questions on connecting to a PLC I would be glad to answer them, as this is often half of the battle when you are new. I spent a week learning to connect to different PLCs and trying different cables (like serial to usb). There are a TON of modules out there, but each one has a specific purpose and protocol.
3. For any kind of PLC network utilizing older protocols/hardware you will need some kind of device to keep track of the other devices on the network. This device is referred to as a "Master."
4. I reiterate that there are a TON of different protocols and ways to connect. You can, for instance, use analog to connect to a Powerflex drive and control it's speed.