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7. Statement of Communication Functions
Communication Interface
Communication Parameters
To transfer data through communication interface, the settings such as “data bit length”, “parity”, “stop bit” and
“baud rate” must be configured first. These settings are collectively referred to as communication parameters
and can be regarded as communication protocols at the hardware level. The communication parameters must
be consistent for all communication devices in a system.
In the eld of industrial automatic control, communication between equipment has become an extremely important part.
The abilities to transmit data mutually, collaborate and communicate with each other to complete the control work
together are highly valued. PLCs are the most basic and most common control equipment in industrial automatic
control, and thus naturally it is also very important to enhance their communication capacity.
According to the different model of the VS series PLC, could have 3 to 6 communication ports.
Those are not only equipped to execute the programming, but also vertically uplink with the Human-Machine Interface
(HMI) or Supervisory Control And Data Acquisition system (SCADA) to construct a monitoring network; horizontally, it
can be connected to multiple VS PLCs to operate the distributed control. In addition, can be the master to connect with
peripheral equipments (such as thermostat, inverter, etc.). Therefore, these create a complete control system.
Compared to the company's previous products, the VS series PLC has made great progress in increasing the number
of communication ports, communication speeds, the exibility of application types and user-friendliness.
This chapter is specically for the VS series PLC communication function to provide a detailed description, and provides
useful help when users operate these communication functions.
7-1 Key Points of Communication Functions
7-1-1 Fundamental Object about the Communication Function
The communication interface which can go with the VS series PLC is including the USB, RS-232 and RS-485.
USB interface the most popular interface used on computers. The VS PLC's main units are all equipped ―
with a built-in USB port to be the programming interface of the PLC and that with a speed rate up to 12 Mbps.
RS-232 interface often used in point-to-point short distance (within 15 meters) communication.―
RS-485 interface often used for multi-points long distance communication. Since it provides with multi-points ―
data exchange capability and long distance communication performance; therefore, now is widely used in
industrial control eld.
Communication Protocol
All the device which provided with communication function should have a communication protocol to support
data transmitting with other equipment.
The communication protocol is a protocol at the software level. Through the same communication protocol,
can reach the purpose of data exchange between different devices.
A communication protocol usually consists of starting character, station number, communication
command, data content, end character, check code, and so on. Of course, each device will dene the
appropriate communication protocol according to its communication needs. Meanwhile, some equipment will
follow the commonly used communication agreement on the market and the MODBUS is undoubtedly the most
common one.
Communication Principles
When two or more devices exchange data between each other, these devices must be linked together to form a
communication circuit. Moreover, this communication circuit needs to follow the basic principles below to start
working:
Have consistent communication interface.
Have consistent communication parameters.
Have consistent communication protocol.
The communication circuit must have a main leader, and only one at a time.
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