Telecommunications system for programmable logic controller

A telecommunications system disposed in a programmable logic controller (PLC), comprising:

• a master device comprising a transmitter and a receiver;
• one or more slave devices, wherein the master device is connected to a communication line, the transmitter is configured to transmit a signal through the communication line to the one or more slave modules, and the receiver is configured to receive a response signal through the communication line from the one or more slave modules;
• a signal conversion device connected to the communication line and configured to convert the signal and the response signal transmitted or received between the master device and the one or more slave devices into digital signals;
• and
• a control device configured to control the master device and the signal conversion device and to determine whether there is an error in the signal and the response signal based on the digital signals transmitted from the signal conversion module,
• wherein the control device determines that the error is resulted from a fault in the communication line if a maximum value of the digital signals is below a high-value voltage value and a minimum value of the digital signals is above a low-level voltage value.