PLC/Panelmate communication

Hello,
I am new to plcs. I'm having trouble understanding how the panelmate and plcs communicate. I have several electrical drawings for different components of a machine. In each drawing where it shows panel mate connections, the panelmates are just connected to the modbus plus 984-145 processor. Can someone please explain how they communicate with each other? I would appreciate any help. Thanks.

The PanelMate reads data from and writes data to the PLC over the Modbus Plus communications cable.

Thanks. That's what I was thinking. Is this the same way for panelmate to robox? And if so are they usually connected the same way. I have a drawing for one part of the machine which shows the connections between the panelmate and robox but I don’t have one for the other part. Could they be connected in a similar way?

I don't know what a robox is, but all PanelMates pass data between themselves and their PLCs over some sort of communication cable. It could be a point-to-point RS232 serial link. It could be a multi-drop RS485 serial link. It could be a network cable like Modbus Plus.