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Precautions for Connecting Communication Devices
When connecting communication devices to the MicroSmart, take possible external noise sources into consideration.
In a communication network consisting of a MicroSmart and an external device (a communication device which has a
functional ground and a signal ground connected together internally [for example, IDEC’s HG3F and HG4F operator inter-
faces]), if all devices are powered by a common AC or DC power source, noise generated by the external device may
affect the internal circuits of the MicroSmart and the communication device. Take the following measures depending on
the operating environment.
Use a separate power supply for the external device generating noises so that a loop circuit to induce noises can not be formed.
Disconnect the functional ground terminal of the communication device from the ground line. This measure may result in deteriora-
tion of EMC characteristics. When taking this measure, make sure that the EMC characteristics of the entire system are satisfactory.
Connect the functional ground terminal of the communication device to the 0V line of the power supply so that the noises from the
external device do not flow through the communication line.
Connect an isolator to the communication line so that a loop circuit to induce noises can not be formed.
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