Connecting to Modbus Device


There are two Modbus protocols you can connect with: Modbus RTU over TCP and Modbus TCP. Typically, you connect using the Modbus TCP driver.

Video recorded using: Ignition 7.9


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[00:00] Let's connect to a device with one of Ignition's Modbus drivers. We're looking at the Configure section over my gateway here. If I scroll on down, you can see that, the page we're on, is under the OPC-UA Server section and Devices. Now if we head back up to the top, you can see I currently do not have any devices configured at all. Let's begin by clicking the create new device link. The next page will contain a list of all of your installed drivers. I'm just going to scroll on down here to the Modbus section. And you see that there are two options I have available. In most scenarios, you'll probably be using the Modbus TCP driver here. However, if you know you're working with an RTU, the Modbus RTU over TCP driver is what you should select. If absolutely uncertain, try both. The RTU driver will only connect with RTU configurations. I know I'm not working with an RTU, so I'll select the Modbus TCP driver. Now let's scroll on down to the bottom of this list and click the Next button.

[01:05] Here we need to give the device connection a name, so I'm just going to call this Modbus. And I'm going to scroll down a little bit more, and under Connectivity, we need to specify a Hostname here. Now I have that saved on my clipboard already, so I'm just going to paste that in. And that's actually all we have to do here. However, I do want to talk about a couple different properties. First, the port defaults to 502. Typically, this is the default port for Modbus TCP over IP. So in most cases, you can leave this setting alone. However, if your device is configured to communicate over a different port, you can specify that here. Additionally, if you check the Show advanced properties checkbox here, scrolling down, you'll see a large list of other properties. Most of these properties can also be left alone, but one important property to point out would be the One-based Addressing here. The driver defaults to one-based, meaning that the address range will start at one. However, you can toggle this property to start the address range at zero instead. The device I'm trying to connect to is one-based, so I can leave this setting alone.

[02:05] The next property down, Span Gaps, optimizes requests by grouping them into large chunks, but if a bad address is present in that range, then every other address in that request will also be flagged with bad quality. This leads to a large amount of bad quality tags that appear in the tag browser. In this scenario, toggling Span Gaps can aid in finding those bad addresses. So I'm going to scroll back on up here. I'm going to uncheck the Show advanced properties here, and I'm just going to click the Create New Device button. On the next page here, we see, we start off with a Disconnected status, and momentarily it switches over to Connected. And that's it. Now that we're connected, we can start creating tags manually or with Ignition's address mapping feature. We'll see examples of both methods in upcoming videos.

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