It’s generally important to know who you are speaking to. I’m sure you’ve had those embarrassing situations where you make a remark and then find out that there was someone in earshot who, had you known, might have caused you to exercise some restraint. I’ve had those cringe-worthy moments on more than one occasion. Oh, if I could just take back some of those comments.
In the networking world, knowing the device you’re connected to is also extremely important. You can run into all sorts of problems if you can’t get identity information from a device. For example, it might be important to know that the device you’ve connected to is not the same one you were connected to prior to that last power cycle. It might be important to know that it’s been upgraded or replaced. It might also be important to know the revision number of a device – you might be able to avoid connecting to a device with known security issues. Some devices have location information. It might be important to know that you’re connecting to a device in a certain location. There are many reasons to read device identity information.
This hasn’t been an issue in the past. Sensor bus networks were by design limited to a local bus. Ethernet networks like ProfiNet IO, EtherNet/IP, and Modbus TCP, while on Ethernet, were generally on an isolated network. But now, given the way that we are integrating factory floor technology with IT, that’s no longer the case. It is now quite possible to have remote devices that are going to interrogate these Ethernet devices, and when they do, they want to read their identify information.
In Profinet, the Identification and Maintenance (I&M) facility requires all Profinet end-devices to provide very extensive identity information. Though it’s been part of the ProfiNet specification since the beginning of time, it’s not a facility that is well-known in the Profinet user community. That’s not unexpected, as most applications are only interested in moving cyclic I/O data between an end device and a controller. Over the years, with a fixed controller exchanging I/O data with a set of specific end-devices defined by the system designer, there wasn’t a need to read Identity information. Most applications never used any acyclic commands to read parameters or configuration information. Conformance testing verifies that a device supports the required acyclic commands but that was usually the last time the device received an acyclic command.
Understanding the I&M interface has become more important as Profinet devices are integrated into larger systems. To understand that interface requires a good understanding of both the Profinet device model and the Profinet address model. This is often a point of confusion for a many people.
The Profinet Address Model describes how a device and its contents are addressed on the network. In Profinet, all devices appear to be remote I/O racks and are addressed using I/O rack terminology: station number, slot, and subslot. The station number addresses the rack as a whole. The slot number addresses the slot within the I/O rack, and the subslot addresses I/O points within the slot, sometimes called channels.
The device model, on the other hand, is all about the contents of those slots in the I/O rack. In the physical world, modules occupy those slots: a 16 point input module can fill slot 1, a 16-bit analog output module can fill slot 2 and so on.
When designing a Profinet device that isn’t a remote I/O rack, you must still organize the interface to the ProfiNet controller as if it is a remote I/O rack. That means that, whatever the data or I/O that end device has, it must still look like an I/O rack. Yes, it seems odd, but you have to organize the interface to things like barcode readers, meters, and drives as it they were I/O racks.
But no matter what the address and module organization is, the I&M facility provides identity information about both the address and device model of that end device. Specifically, it can be used to provide device-level information about the entire device or module level information about the module in terms of its slots and subslots.
The I&M facility benefits the user in different ways:
• It provides “type plate” information that MES systems might use
• It provides identity information that Configuration and Commissioning tools can use
• It provides identity information that visualization programs can use to label screens
I&M data is subdivided into different blocks (IM0 … IM5) and can be addressed separately using indexes. Every IO-Device must support the IM0 function with information about hardware and firmware versions.
The IM0 data block is the important one. All Profinet devices must support it as it provides basic identity information such as:
• MAC address
• Hardware Version
• Software Version
• Product type
• Manufacturer ID
The complete specification for the I&M functionality (Identification and Maintenance specification) can be found on the Profinet International website. Unfortunately, it’s not an easy read. If you’d like to know more, give us a call at RTA and we can help you to understand this complicated component of ProfiNet technology.