The relay outputs of the servo drive can be used as NPN or PNP outputs. In this example, the NPN variant is used. They can be read with the S7-1200 CPU by an inverse power supply connection of the digital inputs (ground terminal of the connection to common potential, 1M, is supplied with L+). If logic “1” is present at the digital output of the drive (the switch shown symbolically in Figure 2-4 is closed), the current “I” is flowing. The S7-1200 CPU interprets the current as logic “1”.