Creating a heartbeat tag in CompactLogix to keep track of communication

Rob S. · Jan 17, 2017

Good Evening ,

I have 2 CompactLogix PLC's , that I am going to use Produced / Consumed Tags . I would like to tell if both are communicating , and if not create a fault. How do you create a system or clock bit in a CompactLogix ? I remember in the SLC 500 , I thought , that you had S: bits that would do similar things .

Thanks in advance ,

jknels01 · Jan 17, 2017

I use UDT's which include connection status as part of the data.

keshik · Jan 17, 2017

Create a UDT to transfer back and forth. Make sure that the first element of the UDT is of data type "CONNECTION_STATUS". There are two BOOLs inside it that will be automatically updated. You can then put whatever else in the UDT that you would to transfer, such as a DINT array.

ASF · Jan 17, 2017

The posts above are how I do it too.

But, just to answer your original question, there are no "clock bits" on the Logix 5000 platform. I have an AOI that I import into all my projects to give me flashing bits, timing pulses and the like, should I need them.

rupej · Jan 17, 2017

Alternatively, if you don't like using UDTs, you can just create a DINT in each PLC called "Changing_Value" or whatever. Have each PLC increment their own value every scan. Monitor this value on the other PLC, and if the value doesn't change for x seconds, then you have lost the connection. That's the way to do it without the S bit from RSL500.

Rob S. · Jan 17, 2017

You can still create a UDT while online , correct ?

ASF · Jan 17, 2017

Yes, you can create/edit/delete UDT's online, as long as they're not being used. So if you create a UDT and then create a tag of that type, you can no longer edit the UDT online. If you need to change it, you either have to do it offline and download, or delete your tag, edit the UDT, and re-create the tag.

A little bit of messing about, but it'll get you there.

lostcontrol · Jan 17, 2017

Does the connection status indicate connected if the PLC is not in run mode..?
If so, then a changing value is the best bet, IMO

dmroeder · Jan 17, 2017

Connection status does indicate run mode.

I don't think you can create produced/consumed tags online. At least you couldn't in the past.

ASF · Jan 17, 2017

lostcontrol said:
Does the connection status indicate connected if the PLC is not in run mode..?
If so, then a changing value is the best bet, IMO

Yes, the CONNECTION_STATUS gives you two bool's - ConnectionFaulted (which should be off for a healthy connection) and RunMode (which means the target PLC is in run mode, and should be on for a healthy connection).

Even if both PLC's are in program mode, these tags will still accurately reflect the state of the connection and the mode of the PLC.

Rob S. · Jan 18, 2017

Thanks for all your advice. Also , can you create Produced / Consumed Tags while online ?

cwal61 · Jan 18, 2017

In RSLogix 5000 Help file\Contents. under the INDEX Tab Type: New Tag dialog box overview

You can create base tags and alias tags while the controller is online or offline, as long as the new tag is verified. You can only create consumed tags while the controller is offline.

Choose this type if you want to make this tag available to remote controllers through controller-to-controller messaging. This parameter is unavailable when online; you must be offline to choose to produce a tag. This parameter is also unavailable for tags that cannot be used as producers

You will also find the setup information on new tags.

Creating a heartbeat tag in CompactLogix to keep track of communication

Rob S.

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jknels01

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keshik

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ASF

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rupej

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Rob S.

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ASF

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lostcontrol

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dmroeder

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ASF

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Rob S.

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cwal61

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