This lesson is part of the Tags in Ignition course. You can browse the rest of the lessons below.


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In order to address bits in Ignition, separate OPC Tags must be created pointing directly to a specific bit in the PLC.

Video recorded using: Ignition 7.7


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[00:00] It is very important to be able to address an individual bit of a word in a PLC. So here in ignition in my tag browser, I have two tags from my ControLogix PLC and my MicroLogix PlC. And I went and browsed for those tags. Well I'm bringing back the entire word here. So, certainly on a screen I can view individual bits, that's not a problem. The problem happens when I want to write a value to a specific bit of a word. And that, if I leave it as integer here, I'd have to some how mask out that right, and hope that only that is that one bit is what I'm changing when I wrote that down to the PLC. So with Ignition, you have to create a separate tag for every bit you want to write down too. So, it's really easy to address a bit. All you got to do is on a tag is double click on it to edit it, and you can change the OPC item path, with all of the Ignition's drivers you can add, an extra piece of information at the end of the item path to address one of the bits. So here on my ControlLogix PLC. I am referencing this level PV. I can put a dot 1 at the end to reference the second bit of that word. Soon as I do that, I need to go up here to my data type and set that to a Boolean, so now, everything is correct. If I go and press OK, I'll see that it is now a Boolean, and it will toggle as that value is changing in the PLC. So now I'm looking at just one bit of that word for the ControlLogix. On the MicroLogix here, this is the overall integer word. This time I'm going to copy, and I'm going to paste that tag so I have two of them. The second one is going to be the bit address. So I'm going to go ahead and double click on the second one, go and change this to a dot 0 to reference the first bit of that word. Make it a Boolean here. So as soon as I do that, you'll see that that is now true. Of course, because, it's a 5, so that first bit is, is high. If I now go in here and uncheck this, I'm going to right, basically going to write a zero to it, I will see that the MicroLogix, the original raw value, is now 4. So if I set it, it's going to go back to 5. And same thing happens if, if I was to change the overall integer word, and I change this, let's say, to a 9, then I would see, I could possibly see this, just toggles. Right now, I'll set it to a 10, I'm going to see it go off there. So, it is possible to address individual words here, and it's really important when writing down. Now some of the PLCs actually support getting down to the bit level, from the browse. So if I go and browse my PLCs, the MicroLogix in particular, if I go to any tag that has bits inside of it, I can expand that tag to see all the individual bits, and I can drag those into Ignition. So, that's all it's too basically looking into individual bits.

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