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 8.1


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[00:00] It's really important in Ignition to be able to address individual bits in a Word. Here you can see I have two Tags, the Controlling and MicroLogix Tag that have some values associated with them. Reading or displaying individual bits of a Word on your screens is very easy to do. But what if you want to actually write to those to do this, we will need to change our Tags or add additional Tags to be able to show just the individual bit and then we can write to it very simply. It's easy to alter an existing Tag like this ControlLogix Tag. I can just double click on it to open up the Tag Editor and then I can change my OPC Item Path to show just the individual bit. You can see I'm looking at this T1 level PV Tag and I can go and add a dot one to the end of the OPC Item Path. And that will give me just that first bit. Now, if I do this, I'll also have to change the data type from short to Boolean. And then if I click apply down at the bottom, then you can see now my ControlLogix Tag and the tag browser changes to just a Boolean value and you can see a turning on and off based on how the Tag is changing. Now I can do the same thing for my MicroLogix here. I'll actually go ahead and duplicate I'll copy and paste, so I get a second one. And again, I can double click on this new Tag. I can change my OPC Item Path for this Tag in the same way. I'll put dot zero at the end to get the very first Bit, and I'll also change that data type to Boolean. Now, when I hit apply, you can see that my new MicroLogix one Tag has a value of True because our Micro original MicroLogix Tag has value of five. If I set this new Tag to False, then you can see that our MicroLogix Tag changes to four. Now I can also change the value of the Tag to something like 10. And if you change it to 10, you can see our value is still False. And if I change it to nine, then it changes back to True. Now some PLCs will actually support getting a value all the way down to the Bit-level. So if I go and browse my device here and I go into my MicroLogix and into my end seven, then you can see each of these individual Tags will allow you to select a particular bit. And then you can add those to the Tag browser.

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