Machine ( HMI） An overview of the serial communication with PLC

the man-machine touch screen ( Hereinafter referred to as the HMI) , the use of NEO - is its own development RTOS operating system, has experienced 15 years continuously updated, independently developed a good and stable configuration software platform, especially in the response speed of communication with PLC and screen display, etc. As man-machine generation of HMI, HMI in the industrial field running reliability, praised by users, users generally feel that the benefits of a series of HMI can be connected to the PLC system.

1。 HMI and PLC to realize the significance of communication

the HMI is connected to the PLC application system function has the following four aspects:

1) Constitute a HMI as the upper machine, single or more small distributed system of PLC for the next bit machine, available HMI operation station functions.

2) In a PLC application system, the HMI development into simple workstation or terminal industry, which can realize centralized display, centralized alarm and data collection function.

3) The HMI development into many sets of similar or different PLC data transfer terminal, can be through the communication interface interface to access many sets of PLC, similar to or PLC of the heterogeneous data exchange.

4) Connector (between the HMI development into a net Gateway functionality) For protocol conversion, which can realize PLC and other computer or other HMI network connectivity.

another for multipoint structure, HMI and PLC, and more than even in the same serial bus, as shown in the figure below. Multi-point master-slave access control method, the structure is usually given priority to with HMI station, many sets of PLC is from the station, through periodic polling communication management. Siemens S7 - for example 300 the MPI communication, HMI can more screen PLC to form a communication structure.

2。 Method of HMI and PLC communication

the HMI is connected to the PLC application system in order to provide such as process flow diagram shows, dynamic data showed, trend graph generated, window technology and production management and other functions, for PLC application system provide a good, inexpensive man-machine interface.

in order to realize the HMI and PLC communication, users should do the following work:

1) Identifying whether the communication port on the HMI configuration and PLC to be connected to match, if not match, increase communication module, general hardware entity communication port for the RS232 / RS422 / RS485.

2) To clear the PLC communication protocol, in accordance with the provisions of the agreement and HMI communication. Equipped with a PLC communication mechanism, generally do not need programming by the user. Machine programming software PM Designer ( English: touch the master) Of special communication protocol of PLC, user can very easily the HMI and PLC communication, need not in written communication program.

3) Use the programming software man-machine PM Designer software platform, using the frame and function of the PC user requirements.

in principle, HMI and connected to the PLC network without any difficulty. As long as the HMI can be equipped with this kind of the mouth and the PLC of the same communication protocol, the connection mode of connection, according to the requirement and the programming software set parameters, download you compile program to HM. The benefits of using this method the HMI connected to the PLC network is very cheap price. For example, using a PC with PLC manufacturers in the production of special communication card and special communication software, than use a HMI to connect the PLC to higher price several times or even dozens of times.

the first user generally interested in the question is, can use the HMI is generally equipped with serial communication the HMI connected to PLC, which is in this section will focus on the problem.

with serial communication interface of HMI and PLC communication does not have to work, only to meet the following conditions can realize communication.

1) Only with a serial communication interface of PLC and the way of serial communication of PLC network is possible and HMI interconnect with serial communication interface. At the same time also require the use of bus standard should agree, for instance is RS - on both sides 232 c, or are RS - 422 ( RS - 485). , or to pass the 'bus standard transformation units' ( Conversion adapter) After transformation to interconnect. In addition, the reasons for the success of communication are the most common communication cable connection error, please refer to the manual of HMI and PLC manual wiring connections.

2) Will on both sides of the initialization, baud rate, data bits, stop bits and parity are the same, and set the PLC station number.

3) User must be familiar with the Internet is the communication protocol of PLC. Strictly in accordance with relevant provisions of the agreement to choose the same communication protocol in the programming software. Now many PLC at the same time with several types of communication protocols, users need to choose a in the PLC and HMI communication.

meet the above three conditions, HMI can be interconnected communication with PLC. If you cannot meet these conditions cannot achieve interconnection.

4。 The structure of PC and PLC connected

the HMI and PLC controller with asynchronous communication adapter are interconnected communication usually take the form of two kinds of structure as shown in the figure below. A structure for point-to-point, HMI and PLC programming of the COM interface ( Must be a serial communication port) A point-to-point link between the implementation.

the man-machine HMI have multiple serial ports, and, when necessary, will be able to connect two or more HMI and PLC, HMI were formed connection structure of a PLC, HMI to develop fully functional, the PC to develop it into a PLC programming terminal, HMI can be become a programmer interface connected to the PLC programming, debugging, and monitoring.

HMI have multiple serial ports, the other can be simultaneously connected to two or more different types of PLC, can through the HMI transfer, so can make the two different types of PLC data exchange.

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