Hello everyone! I have a question regarding the use of Message Instructions in our communication setup. I understand that only one Message Instruction can be active at a time. In order to establish a sequential order, I utilized counters and timers with the Modbus RS485 network channel. However, we’re now transitioning to Modbus TCP and will be utilizing a different communication port (Ethernet TCP/IP Port). My question is: do the new Message Instructions for Modbus TCP need to adhere to the existing sequential order established for the Modbus RS485 network? Or, since we are using a separate port for communication, is it unnecessary to follow the previous Message Instruction sequence? Thank you for your assistance!
Are you asking whether you need to wait for a response before sending a new request? When utilizing RS-485 or RS-422 communication protocols, the answer is yes; each request must wait for a response before proceeding. However, with MODBUS TCP, the master device assigns a unique sequential identifier to each request. The responding slave device then echoes this identifier in its response, allowing the master to determine which request the response corresponds to. In theory, this system enables the master to send multiple requests in quick succession without waiting for individual responses. However, it's important to note that not all slave devices may respond optimally in this manner; the only way to be certain is through testing. Additionally, keep in mind that this setup may not necessarily lead to a significant increase in transmission speed in all situations. I hope this information is helpful!
Lfe asked: "Are you saying that when you send a request, you must wait for a response before sending another request?" In response, I explained that when using RS-485 or RS-422 communication protocols, the answer is indeed yes; you must wait for a response after each request. However, with MODBUS TCP, the master device assigns a unique sequential identifier to each request. The slave device then copies this identifier and includes it in its response, allowing the master to determine which request each response corresponds to. In theory, this method enables the master to send multiple requests in quick succession without waiting for a response after each one. Yet, it's important to note that not all slave devices may function well under this scenario, and the only way to confirm performance is through testing. Additionally, it may not necessarily result in a significant increase in transmission speed in every situation. I hope this clarifies things. So, to confirm, is the RS-485/RS-422 communication port different? Can the RS-485/RS-422 port simultaneously send and receive messages like the MODBUS TCP port, considering they operate on different protocols and networks?
RS-485 is a half-duplex communication standard, meaning it cannot send and receive data simultaneously. This limitation arises because it utilizes the same transmission pair for both directions. In contrast, RS-422 supports full-duplex communication, allowing for simultaneous sending and receiving of data. However, this capability holds true primarily in a one-to-one communication scenario. When it comes to a one-to-many configuration (such as one master communicating with multiple slave devices), the potential for data collisions increases significantly if multiple slaves attempt to respond at the same time.
Life explained: RS-485 operates as a half-duplex communication protocol, meaning it cannot transmit and receive data simultaneously due to the use of the same transmission pair for both directions. In contrast, RS-422 supports full-duplex communication, allowing it to send and receive data at the same time; however, this is fully applicable only in scenarios involving one-to-one communication. In one-to-many setups, such as a master communicating with multiple slave devices, collisions may occur if more than one slave attempts to respond simultaneously. Now, let's discuss the Modbus TCP port, which operates over Ethernet. Can this port handle simultaneous transmit and receive operations while the RS-485 port is in use? Is it possible for these two distinct ports to interact concurrently?
TCP utilizes a connected socket to create a bidirectional channel that allows for simultaneous data transmission and reception without limitations. This technology ensures efficient and real-time communication across networks.
Great question! When transitioning to Modbus TCP, you have a bit more flexibility since the protocol's implementation and the communication medium are changing. While it’s generally a good idea to maintain the existing sequential order for consistency and to avoid confusion, there's no strict requirement to adhere to it just because you're using a different port. It might be beneficial to reassess the requirements of your new setup and see if any adjustments or optimizations can be made based on the capabilities of Modbus TCP. That could lead to improved performance or simplified logic!
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