Hello everyone! I'm a beginner in PLC programming and have recently developed a ladder logic program using RSLogix 500. Currently, I want to send an input from one PLC and receive the output on a second PLC. For this setup, I am utilizing two MicroLogix 1400 controllers connected via Ethernet cable. I understand that I need to implement the MSG (message) instruction, but I could use some guidance on how to effectively use it. Thank you in advance for your help!
Welcome to the forum! I have a question: is this assignment for homework or a work-related project? This task consists of several components: 1. Transfer the inputs to a file that can be utilized in the message instruction. 2. Establish a heartbeat signal between each PLC (Programmable Logic Controller). 3. Implement the message instruction to facilitate communication between each PLC. 4. Save the file to the outputs. It's important to note that the connection between the PLCs must be made through a switch or by using a crossover cable. A standard Ethernet cable will not suffice for this setup, as far as I know. Please download the instruction manual to familiarize yourself with the message instruction. I'm not the most qualified to assist with the message instruction, but feel free to share your progress, and we will provide helpful suggestions. Best, James
Thank you for your response! As I mentioned earlier, I am new to PLC (Programmable Logic Controller) systems. Currently, I am focused on implementing basic functions to familiarize myself with the MSG (Message) instruction. Once I gain a better understanding, I will be able to make the necessary adjustments. I've attached screenshots for your reference. In the first PLC MSG setup screen, I have entered the address of the second PLC in the Multi-hop tab.
To enhance your automation project, consider establishing a consistent method for designating 'N' registers as the source and destination for read and write operations within messages. On the 'input' PLC, utilize straightforward ladder logic to transfer the necessary input states into an N register (for instance, mapping I:0/0 to N7:10). If the destination N register on the receiving PLC is N7:11, the MSG command will transmit the value from N7:10 to N7:11. Subsequently, the 'output' PLC can easily transfer the data from N7:11/0 to O:0/0. In summary, the input PLC compiles the real input values into the N register, then sends this information via the MSG command to update the N register on the output PLC. The output logic translates the N register information into actual outputs. Keep in mind that communication can also flow in the reverse direction. I recommend designating one PLC as the 'master' to handle all reads and writes, as this can minimize confusion. Additionally, implementing a handshaking protocol is advisable. This approach allows the output PLC to verify whether the data in its N register is up to date and to deactivate outputs if there is a loss of communication. We encourage you to explore setting this up independently first.
User bernie_carlton recommends developing a routine for designating 'N' registers as the sources and targets for reading and writing messages. In the 'input' PLC, it's beneficial to create straightforward programming rungs that transfer the required input states into an 'N' register (for example, I:0/0 to N7:10). If the receiving PLC utilizes N7:11 as its 'N' register, then the MSG command will facilitate the transfer of data from N7:10 to N7:11. Consequently, the 'output' PLC can easily copy the information from N7:11/0 to O:0/0. To summarize, the process involves the input PLC storing actual inputs into an 'N' register, while the MSG command conveys this data to the output PLC's 'N' register. The logic program in the output PLC then converts the 'N' register information into a physical output. This communication flow can also operate in reverse. Personally, I find it less confusing to designate one PLC as the 'leader' for handling all reads and writes—though the choice is ultimately yours. As previously suggested, implementing a handshaking method is advisable. This enables the output PLC to verify whether the data in its 'N' register is 'current', which is crucial for managing output shutdowns during communication disruptions. We encourage you to explore this topic on your own. Thank you for your input! I’ve successfully stored the input and output values in the integer file and am curious about entering the same integers into the "data table address" fields for both the controller and target device in the MSG setup screen.
James McQuade stated: "Welcome to the forum! I have a quick question: Is this task related to homework, or is it part of an actual work project? This assignment consists of several steps: 1. Transfer the input data to a file that can be utilized in the MSG instruction. 2. Establish a heartbeat signal between each PLC (Programmable Logic Controller). 3. Construct the MSG instruction for communication between the PLCs. 4. Save the file to the output devices. It's important to note that the connection among the PLCs must pass through a network switch or use a crossover cable; standard cables will not be effective in this case, to my knowledge. I recommend downloading the instruction manual and familiarizing yourself with the MSG instruction. While I may not be the best resource for this specific instruction, please showcase your progress, and we will provide constructive feedback. On a side note, this is indeed an actual work project I recently began at a new company, and I've been assigned this task. I've tried searching online for guidance on implementing the MSG command in RSLogix but have struggled to find any comprehensive resources that detail the process."
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Answer: 1. Open your RSLogix 500 project and go to the ladder logic where you want to implement the MSG instruction. 2. Insert the MSG instruction into your ladder logic program. 3. Configure the MSG instruction's parameters. You'll need to specify the message type (such as read or write), the target controller's IP address, and the data file locations for both the source and destination. 4. Ensure both PLCs are properly connected via Ethernet and that their IP settings are correctly configured for communication. 5. Download the program to both controllers and test the communication setup to ensure data is being sent and received as expected.
Answer: - Incorrect IP address or communication settings, which can prevent successful data transmission. - Mismatched data
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