not all tags in RSLinx Enterprise

I am a beginner learning how to use Factorytalk View ME Studio. The tag browser shows the connected PLC's tags; I can see all the tags except that I see a word level tag for B3:0. I have multiple bit level instructions (B3:0/0, b3:0/1 and b3:0/2) in the PLC program. I cannot expand the B3:0 in the tag browser to use the bit level addresses. The fact that I see all other tags tells me that I had configured the RSLinx Enterprise correctly. I will attach some screen shots of the tag browser in the next reply posting.

I am going to try to browse offline tags next, but I first want to know how I can solve this online tag problem. Thanks.

As you can see in the posted pictures, the input addresses are expanded bit level addresses, but the internal coil address is a word level and not expandable.

Also, why there is no "offline" folder? The manual for FTV Studio states "For each RSLinx Enterprise shortcut in an application, an Offline and Online folder is displayed in the Tag Browser." Thanks.

The tag browser does not browse to individual bits within a word. You aren't doing anything wrong. Its just how it works. You would need to type the specific bit number you require.

Offline tag files must be specified in the Communications Setup portion of RSLinx Enterprise. If you don't specify the offline tag file then the Offline folder is not displayed in the Tag Browser window.

However, that feature is specific to the Logix 5000 family. The Offline Tag File feature does not support your MicroLogix.

OG

Follow this link for information about creating tags from an offline RSS file.

Operaghost said:

The tag browser does not browse to individual bits within a word. You aren't doing anything wrong. Its just how it works. You would need to type the specific bit number you require.

Click to expand...

Hi OG, so I just need to type in the bit level address to change from {::[micrologix1100]B3:0} to {::[micrologix1100]B3:0/0} ?

Thank you so much OG and Bernie. I have another question if I may.

I am more familiar with Panelbuilder32 where I had to type in the tag addresses in the tag browser and I never used input and output addresses. So, the first time I saw the device tags in the FTV Studio tag browser, I was surprised to see the input and output addresses. I know I can read the otuput address status (as a multistate indicator). But ...

1) can I write an output address tag (to turn on the output module terminal directly)?

2) Can I write an input address tag (to turn on the input module terminal directly)?

3) Can I read an input address tag?

Directly addressing I/O registers is possible, but comes with a handful of complications.

First, the direct answers to your questions:

1) Can I write an Output address tag (to turn on the output module terminal directly)?

Yes. If there is logic in the controller that also determines the state of that output address, the logic in the controller will over-ride the value you have written almost immediately. If there is no logic in the controller for that address, the state will be applied to the output terminal.

2) Can I write an Input address tag (to turn on the input module terminal directly)?

Technically yes but practically no. The actual value of the Input terminal will be written over the value you write to the data table almost immediately.

3) Can I read an Input address tag?

Yes.

You'll note that I used the phrase "almost immediately" twice.

I haven't made a close study of the MicroLogix operating system lately, so I cannot say for sure whether the incoming communications packets or the I/O scan is performed first.

So I'm not sure if writing directly to the Output data table would cause no change to the output, or if it could change for a fraction of a millisecond, or if it could change for one whole PLC scan.

Also, the addressing syntax for physical I/O can be tricky: you can address it by absolute offset or by word. There are threads on the Forum where people talk about this at length, in particular regarding MicroLogix.

And remember that if you accidentally write a value to an unused-in-logic Output data table bit, it stays there until you write an opposite value. I've accidentally turned on physical loads and scrambled to open up the data table editor window to write the opposite value while the motor was turning, pumping product on to the floor.

Some guys actually buffer their I/O through an abstraction data layer, making it easier to re-route stuff later if you burn out a single point.

For all of these reasons, while it's technically possible to read and write the actual Input and Output data tables, I generally recommend against it.

Not likely an issue for our original poster, but just in case others come across this later....

Some of the earlier model SLC 500 processors had protection applied to their Input and/or Output files which would prevent the HMI from writing directly to these files.

While all models support this protection, these early models had this protection turned on by default.

OG