![]() All of these combined make troubleshooting far easier and faster with a PROFINET network. Finally, PROFINET specifies the use of LLDP (Link Layer Discovery Protocol) for further network diagnostics, such network topology. And this allows further diagnostics for network statistics (network load, CRC errors, etc.). In addition, many PROFINET devices also support SNMP (Simple Network Management Protocol) and HTTP (web pages). PROFINET has many diagnostic capabilities built into the protocol for process, device, or network errors. Modbus TCP does not have device diagnostics, it only supports some message handling errors such as protocol communication timeout (message transfer error, device busy etc.). Device Diagnosticsĭevice diagnostics are crucial as they help resolve automation problems quickly. With PROFINET, the vendor describes the data in the GSD file of their device and this gets mapped into the memory of the controller for access in the user application program. PROFINET has many forms of data representation including bits, bytes, words, doublewords, real numbers, strings, and more. Modbus has two data types for data representation: a coil (bit) or or a register (word). This makes setup much easier than having to write special PLC code or setup blocks just for the communications. Each PROFINET vendor provides a general station device description (GSD) of their device which is used to bring in the device in order to configure it in the engineering tool. PROFINET is a configured communication, and only in special cases would require programming in code (e.g. Modbus TCP is a programmed communication which has to be set up in the PLC code via programming function, block, or tool. ![]() Also, it does not support high-speed motion control. Modbus TCP is typically used with process applications because the timing is not critical, but you have to be more careful when planning for factory automation. When it comes to application breadth PROFINET can work for factory, process, and motion control applications simultaneously from the most simple, to the most complex. (ex: 10% above allocated time) With Modbus TCP, there is not a specified performance factor, and there is no specified timing for this process and the handshaking mechanisms. During testing, this speed is monitored and cannot deviate outside allowed tolerances. Speed is also quite fast with PROFINET as typical IO devices can run at 1ms update times with minimum cycle times from the standard of 31.25uS with the fastest motion control devices. This is handled by each device being a provider of data, and a consumer of data at the same time, the controller sends the output data, devices send inputs. With PROFINET IO full duplex, each device sends its data on its own without waiting for the partner thereby taking advantage of the Ethernet standard. In addition, Modbus TCP packs its IO data and wraps it inside of a TCP/IP message, which makes transfer time longer. A client must first send a request to a server, then the server answers this request for every transaction. Half duplex is a request/reply or ‘polling’ type of communication that makes the communication slow and laborious. You may ask what is big deal with that? Well, one is the fact that Modbus TCP uses half duplex communications at Layer 4 of the OSI model while PROFINET uses full duplex at Layer 2. PROFINET uses Ethernet for real time data exchange with a provider/consumer model whereas Modbus uses TCP/IP with a client/server model. When it comes to a comparison of speed and determinism, PROFINET is the clear winner. At the end of the comparison, we’ll show a table highlighting the main points for quick reference. In this article, we’ll explain how PROFINET and Modbus TCP compare head to head in order to help you understand the differences between them. Often, when we talk with customers, they ask how PROFINET compares with other network protocols.
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