PROFIBUS interface is an RS485 serial port, typically using a SUB-D female connector, with the pin definitions as follows:
Pin 3 is connected to the signal line B (red) of the PROFIBUS cable, while pin 8 is connected to the signal line A (green). Pins 2 and 7 provide a 24V power supply which can power the PC adapter, but these two pins are generally not provided in most slave interfaces, making it impossible to use some PC adapters that require interface power, such as the PC Adapter RS232 and PC Adapter USB.
The CPU or CP card also uses this type of interface, where the external metal part of this interface connects to the CPU or CP‘s internal “PE”. When the CPU is installed on the backplane, its “PE” is connected to the backplane. If the backplane is grounded within the electrical cabinet, then the external metal part of this SUB-D interface is also grounded.