I am looking to set up a PLC as a Modbus client to connect to an Arduino acting as the Modbus server. However, I have encountered difficulties during the setup process. I have followed the manual Application Note AH EN MODBUS/TCP but am facing errors at step 5.1.12. The issue seems to be that the variables assigned to the Modbus registers are not included in the I/O configuration. Additionally, I am experiencing challenges using the MB_ASYNC_RW function block. My goal is to create a simple program where the PLC receives values from the Arduino through 3 input variables and sends back 6 variables (3 inputs and 3 outputs, all BOOL). Can you assist me in configuring the PLC as a Modbus client in this scenario? Thank you.
Have you experimented with utilizing a modbus software on your PC to analyze communication protocols?
Sure, I'd be happy to assist. From what you've described, it seems like the issue you're encountering is indeed linked to your I/O configuration. When setting up your PLC as a Modbus client, you'll need to ensure that your I/O configuration includes all of the variables that are assigned to your Modbus registers. This is what allows your PLC to recognize and process signals from your Arduino server. Regarding the MB_ASYNC_RW function block, make sure the amount of read/write parameters matches your intended application (3 inputs & 3 outputs). A common error can be entering incorrect values in the function block parameters, such as the device address, quantity of coils, or the starting address. It can be a tedious process, but debugging function block by function block can usually help isolate and resolve these issues.
Firstly, sorry to hear about the issues you're running into. Configuring PLC as a Modbus client can be challenging but is achievable with the right approach. Let’s tackle this step by step. Regarding the variables, ensure that they are correctly assigned to the correct Modbus registers in the PLC's I/O configuration. Their types should also correspond to what's expected. In relation to the MB_ASYNC_RW function block, could you share the specific bit error you're receiving? It may be due to incorrect addressing or may need to specifically call the function block in your logic. Remember, for your setup, input variables must be defined as Modbus Holding Registers, and the PLC side must be set to read and write to these registers. Be patient, you're a step closer turning your PLC into a Modbus client.
It sounds like you're on the right track, but it can definitely be tricky getting the I/O mapping set up properly. Have you double-checked that the Modbus registers on the Arduino side are properly defined and match the register addresses you're trying to access on the PLC? Sometimes, mismatches here can lead to issues. Also, make sure that the MB_ASYNC_RW function block is being called correctly and that the configuration parameters like the server's IP address and port are accurate on the PLC side. If you're still encountering errors, it might help to simplify your configuration temporarily just to validate the connection—perhaps try reading and writing a single register first and then scale up from there. Don't hesitate to provide any specific error codes you’re seeing; that could help narrow things down!
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Answer: - Errors during setup could be due to variables assigned to Modbus registers not being included in the I/O configuration, as mentioned in step 5.1.12. Double-check that the variables are properly configured.
Answer: - Ensure that the MB_ASYNC_RW function block is correctly implemented in your program. Check the syntax and parameters to make sure it aligns with the communication requirements between the PLC and Arduino.
Answer: - To configure the PLC as a Modbus client, refer to the manual Application Note AH EN MODBUS/TCP for guidance. Make sure to include the necessary variables in the I/O configuration and correctly use function blocks for communication.
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