Customers often ask about the different communication methods between UN200 and UN300, and which is simpler and more stable. Below, I have summarized several common communication methods: MPI communication, PROFIBUS DP communication, and MODBUS communication.
1. MPI Communication:
This is the simplest and easiest communication method to implement. It doesn't even require any additional hardware. You just need to connect the 300 MPI and the 200 485 port (using an adapter from Yiwei or soldering a 1-yuan DB9). However, you need to program it yourself, and the program is extremely simple. This method can connect a limited number of 200 devices, and the speed is relatively slow. The maximum baud rate is 187.5Kbps, which can meet most requirements, but its real-time performance cannot match that of DP.
When UN200 and UN300 use MPI communication, no communication-related programs need to be written in the UN200 PLC. It only needs to organize the data to be exchanged into a contiguous V memory area. In the UN300, the system functions X_GET (SFC67) and X_PUT (SFC68) need to be called in OB1 (or the timer interrupt organization block OB35) to realize the communication between UN300 and UN200. When calling SFC67 and SFC68, the VAR_ADDR parameter should be filled with the data address area of UN200. Here, P#DB1.××× BYTE n should be filled in, which corresponds to the data area from VB×× to VB(××＋n) in the V memory area of UN200.
First, based on the UN300 hardware configuration, configure and download the UN300 station in STEP7. Note that the default MPI address for both UN200 and UN300 is 2, so you must first modify the station address of one of the PLCs, setting the UN300 MPI address to 2 and the UN200 address to 3. Additionally, you must set the communication rate for both UN300 and UN200 to be the same, which can be set to 9.6K, 19.2K, or 187.5K baud rates. Then, configure the SFC67 and SFC68 function blocks.
2. PROFIBUS DP communication
This is the most stable and real-time communication method, but the UN200 requires the addition of an EM277 in terms of hardware. This method is also the simplest in terms of software; you only need to add the 277 GSD file to STEP7 and configure it in the hardware settings.
UN300 and UN200 communicate via PROFIBUS DP through EM277. UN300 station configuration is required in STEP7. In the UN200 system, no communication configuration or programming is required. It is only necessary to organize and store the data to be communicated in the V storage area, which corresponds to the hardware I/O address when configuring UN300 as an EM277 slave station.
Insert a UN300 station, and then import the GSD file. After importing the GSD file, find the EM277 slave station in the device selection list on the right: PROFIBUS DP → Additional Field Devices → PLC → UniMAT → UN 277 PROFIBUS-DP, and select a communication method according to your communication byte count.
After the hardware download for UN300 is complete, set the DIP switch of EM277 to the same value as the above hardware configuration settings. Write a program in UN200 to store the exchanged data in VB0-VB15, corresponding to PQB0-PQB7 and PIB0-PIB7 of UN300.
Note: VB0-VB7 are data written from S7-300 to S7-200, and VB8-VB15 are values read from S7-200 by S7-300. The position of the DIP switch on EM277 must be consistent with the address value configured in S7-300.
3. MODBUS Communication
First, configure the UN300 hardware, then connect it to the UN200 via MODBUS communication using the Yiwei CP341. The Yiwei CP341 MODBUS communication module supports communication with various types of MODBUS devices, eliminating the need for an expensive additional MODBUS hardware dongle, saving users costs. It uses a DB9 serial communication interface, allowing direct connection with the Yiwei PROFIBUS bus connector, eliminating the hassle of soldering wires and making it easy to use. Communication uses opto-isolation, with a maximum communication distance of 1200m. No external 24V power supply is required, making it convenient for users. It supports a wide communication baud rate range: 300-115200bps.
4. Other communication methods
In addition, there are communication methods such as Ethernet and freeport.
