| CPC G05B 19/054 (2013.01) [G05B 19/052 (2013.01); G06F 13/4022 (2013.01); G06F 13/4068 (2013.01); G05B 2219/1109 (2013.01); G05B 2219/1215 (2013.01)] | 8 Claims |

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1. A PLC comprising:
a master unit and a plurality of interface units connected to the master unit through a system bus,
wherein the master unit includes a control unit for controlling an input/output and processing a commands and a plurality of first RJ45 terminals for input/output of data, and a maximum of eight signals are arranged through each pin of each of the first RJ45 terminals,
wherein the interface unit includes a second RJ45 terminal for connecting a signal line from the first RJ45 terminal and a connection means for connecting a signal with an external device,
wherein the interface unit is expandable by the number of the first RJ45 terminals,
wherein the master unit further comprises a plurality of status display LEDs (Light Emitting Diode) for displaying a state of a signal line,
wherein the status display LEDs are classified into a first LED group provided at least as many as the number of the first RJ45 terminals to specify a first RJ45 terminal, to which a signal line to display a state belongs, and a second LED group provided at least as many as the number of pins of each first RJ45 terminal to specify a pin number of the first RJ45 terminal, and
wherein the state of the signal line is output to a predetermined LED of the first LED group and the second LED group at a constant cycle for each first RJ45 terminal.
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