PLC, Arduino, 3 Phase Motor, HMI, Communication

Hi i'm making project about implementing PID on 3 phase motor. It's to hard to use PID on plc and i choose to make the PID in the Arduino to do a 2-way communication with PLC. If i want to connect Arduino Uno with PLC CP1E. What kind of Communication i shall use?

Note: I already use RS232 in plc to connect with HMI. That means i only have arduino and USB Type B in PLC to connect. I also bought MAX 232 because i thought plc has 2 port RS232.

I know this is arduino forum, but i wish someone understand the connection between plc and arduino.
Thanks.

A post was merged into an existing topic: PLC CP1E, HMI, Arduino UNO, PID Communication