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


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Memory Tags are simple Tags, in that they do not automatically update or change value. They are useful for storing values because they are available to subsystems throughout the entire Gateway.

Video recorded using: Ignition 8.1


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[00:00] In this lesson, we'll explain the purpose of memory tags and show how to create and update one. A memory tag is a very simplistic tag. Unlike other tag types, a memory tag doesn't automatically update or change its value from some outside data source, such as a PLC or a database. Instead, it simply stores a data value in memory until it gets updated somehow by other means. Hence its name. It's akin to a global storage variable. Creating a memory tag is no different from creating any other standard tag type. in our Tag Browser, we will simply click on the Add button and select the New Standard Tag > Memory Tag option. This will bring up our Tag Editor. Though there are lots of options here, we'll just update the three basic settings of interest. So we will give our tag a name, perhaps memtag1. We'll leave the data type at its default value of Integer, and we'll give our tag an initial value, maybe 45. We'll leave all other options at their default values.

[01:05] That's enough to set up a simple tag. So we'll click OK. This finishes the tag configuration, and now our Tag Browser shows the specified memory tag. So let's update this tag. Right now its value is set to 45. If we first ensure that our Designer is set to bi-directional read write mode, we can then double click on the tag and set it to some other value, maybe 60. Again, a memory tag retains its current value until something comes along and writes to it. Typically, that's going to be some other component bound bidirectionally to it, or perhaps a script that writes to it. So for example, we could drag this tag to the window, and select a Control > Slider element to write to it. If we set the Designer to Preview mode, we see that dragging the slider updates the memory tag value. Memory tags can be really useful during initial development, if you just need a placeholder tag. For example, say you wanna start a project, but you don't yet have access to any viable PLC data. For the time being, you can simply use memory tags as stand-ins.

[02:10] Or if you want to test the functionality of a script in advance of using live production tags, you can make use of memory tags instead. It's also pretty common to use memory tags, for example, as setpoint tags for alarms, storing the current work order number for a particular production line, or any number of other purposes. Memory tags, like all other tags, reside inside tag providers created on the Gateway. So any other module subsystem or feature of Ignition has access to such tags. The ability for a memory tag to exist independently from OPC or any databases, makes them a powerful and useful part of the Ignition tag system. So now we've seen that memory tags are like items of global memory storage, independent of any PLC or database, and we have seen how to set them up and how to update them.

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