Hardware 3.7 Serial interface COM1 The serial interface mainly provides a connection to pro- gramming PCs. Apart from that it can also be used for communication with other devices such as dialogue termi- nals, for example. Ш Type V.24 (RS 232) Ш Connector female 9-pin D-Sub connector Ш Pin wiring 2 TxD 3 RxD 5 Gnd Ш Cable shielding connects to the plug’s frame ground. The metal connector casing is directly connected to the frame and, thus, to earth if the device is properly eart- hed (see chapter 3.3.2). 3.8 Light emitting diodes Two LEDs indicate the system status:
Ш run/stop lights up green while the PLC program is running lights up red when the PLC program stops Ш failure flashes red if there is a short at an output 30