【Question 1】What is the RS422 interface of the Mitsubishi FX PLC? What are the functions of its communication function expansion board?
【answer】
The RS-422 interface is a subset of the RS-499 interface standard introduced by the EIA in 1997. It defines 10 circuit functions not found in RS-232 and specifies the use of a 37-pin connector. It employs differential transmission and reception, with both the transmitter and receiver using a +5V power supply. Therefore, it offers significant improvements over the RS-232C interface in terms of communication speed, communication distance, and common-mode interference immunity. Using the RS-422 interface, the maximum data transmission rate can reach 10 kbit/s, and the communication distance can range from 12 to 1200 meters.
The FX2N-422BD is an RS-422 communication function expansion board (Figure 1). It can provide an additional RS-422 communication port for FX series PLCs to communicate with external devices that have RS-422 ports. The FX2N-422BD can be installed inside the PLC without requiring external installation space. The transmission distance is 50m, the communication mode is half duplex, and the maximum transmission rate is 19200bit/s.
Figure 1
[Question 2] How to set the parameters for MODBUS communication on a Mitsubishi A700 inverter?
【answer】
When communicating via Modbus RTU protocol, Pr551 must be set to 2, Pr340 to a value other than 0, and Pr79 to 0, 2, or 6. When communicating via RS-485 terminals using the Modbus RTU protocol, it must be operated in NET network mode (as shown in Figure 2). When communicating between the PLC and the frequency converter, the communication specifications must be set in the frequency converter. After each parameter initialization, the frequency converter must be reset or its power supply switched on and off.
Table 1
Figure 2
[Question 3] How to parameterize Siemens CP34x templates?
【answer】
Double-click the CP34x template in the hardware configuration window to open the CP34x template properties window. Please note the hardware address of the template, as shown in Figure 3.
Figure 3
When writing a communication program, the user needs this address parameter, and can click the Parameters button on the properties window.
Figure 4
Figure 4 shows how to select the communication protocol to use. Here we choose the ASCII protocol by double-clicking the envelope icon.
Figure 5
As shown in Figure 5, the ASCII protocol communication parameter setting window pops up. Here we use the default values: 9600bit/s, 8 databits, 1 stopbit, and evenparity.
Save and compile the hardware configuration, then download the hardware configuration. If the SF light is on at this time, connect the communication cable to another communication partner. If the SF light goes out, it means the hardware configuration is correct.
[Question 4] What are the different types of Siemens Ethernet communication? What are the differences between them?
【answer】
1. ISO transmission protocol
ISO transport connections are used for data exchange between S5 stations and S7 stations or PC stations (S5-compatible communication). The characteristics of ISO transport connections are: inter-station communication is based on MAC addresses; data transmission using data blocks is suitable for large amounts of data; data transmission can be implemented using the "SEND/RECEIVE" and "FETCH/WRITE" applications; on the PC, ISO transport services are provided via C functions or by utilizing an OPC server; data reception is determined by acknowledgment from the other party at layer 4 of the ISO reference model; data cannot be transmitted through routers (protocols with non-routing functions).
2. ISO-on-TCP transmission protocol
ISO-on-TCP transport connections are used for data exchange between S5 stations and S7 stations or PC stations (compatible with S5 communication). The attributes of ISO-on-TCP connections include: inter-station communication is based on IP addresses; it conforms to the FRC1006 extension of the TCP/IP standard, which is consistent with Layer 4 of the ISO reference model; and it uses "SEND/RECEIVE" and "FETCH/WRITE" applications to implement data transmission.
3. TCP/IP transmission protocol
Data exchange between stations (including third-party stations) is achieved through TCP connection configuration. TCP connection attributes include: conformance to TCP/IP standards; data transmission can be implemented using "SEND/RECEIVE" and "FETCH/WRITE" applications; existing TCP/IP implementations in the operating system are typically available on PCs; and data can be transmitted via routers (protocols with routing capabilities).
4. UDP transport protocol
Data exchange between two stations is achieved through UDP connection configuration. UDP connection attributes include: UDP protocol; unreliable transmission of associated data blocks between two stations; support for multicast transmission; multicast transmission allows a group of stations to receive and send information together; data transmission via the "SEND/RECEIVE" service; and data can be transmitted via routers (protocols with routing capabilities).
5. S7 Communication
Data exchange between S7 stations and PC stations is achieved through S7 connection configuration. S7 connection attributes: This connection is available for all S7/M7 devices; it is available for all subnets (MPI, PROFIBUS, Industrial Ethernet); reliable data transmission between SIMATIC S7/M7-300/400 stations (using "BSEND/BRCV" or "PUT/GET" SFB); high speed; reliable data transmission depends on the time-dependent operation of the other party (using "USEND/URECV" SFB); data transmission is acknowledged at Layer 7 of the ISO reference process.
6. IT Communications
IT communications have the following characteristics:
(1) E-mail function. The S7 station activates the alarm and sends its text via email. The email may contain variable values and attachments.
(2) HTML Functionality. The CP template includes a web server. Other options, such as applets or JavaBeans, can also be used to provide and view HTML pages with S7 variables. Java applications can access S7 variables via the HTTP protocol through JavaBeans.
(3) FTP Functionality (as Server and Client). The FTP client functionality can be used to save data (from data blocks only) to files on the FTP server, or to retrieve data from the FTP server, only in blocks with a special header (20 bytes). The FTP server functionality is used to transfer files (HTML pages, image files, etc.) to the CP file system, and can also read values directly from data blocks or write values directly from files to data blocks.
7. PG/OP communication
S7 stations are programmed and configured via Ethernet using STEP7. The programming device is connected to the Ethernet.
8. PROFINET communication
PROFINET is a standard used by the PROFIBUS User Organization (PNO). It defines cross-vendor communication and engineering models suitable for component-based automation (CBA) environments.
