The SMD electronics are located in a solid metal 15 pin SubD connector shell. The pin assignment fits the following SIMATIC PLCs: 90U, 95U, 100U, 101U, 115U, 135U, and 155U. The 9 pin SubD connector is plugged into the serial port (COM1 .. COM4) of the PC. The PLC must be active and needs to supply the the loop current (2 x 20mA). If the PLC is passive, the Current-Loop-Converter can be used for power supply.