RobotStudio event

S4C+ common bus interface

Hello, 

I'm designing a pick and place system with one or maybe two used 6600 series arms with S4C+ controllers. I'm hoping to use a PLC to control the robots and other machines in the system. I was wondering what the most common bus system this controller uses to communicate with PLCs. so I can specify the robot and the PLC I'm buying. Thanks in advance.

Jeff