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MODBUS APeriodic Indirect Trigger and Group Trigger


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Ver. 1.25.56

MODBUS TCP is active and working when using the "ID" in Field (B) of a Modbus Aperiodic trigger function, it works. 

When I put the Tag for that same register in the Field (B) it does not work.  Expected I guess as the tag is actual data not an address, but it would be nice if this was linked to the ID somehow. The only way I see around this is to have an entire struct of ID numbers with Tags or use a table to search the desired tag and store the corresponding id into a tag. 


When using the MODBUS APeriodic Indirect Group Trigger to try to get around this, I enter the Group ID entered in the Registers Aperiodic table and it does not work (get a status code 2) 

The only option this is leaving me is to have to remember all the registers by ID?

Registers Periodic work but I need to trigger this register send in the ladder vs sending it over and over again clogging up my network. 


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  • MVP 2023

I poked at the Modbus TCP slave configuration and arrived at the same conclusion.  If you click on a field and the little pencil icon appears then it can accept a tag.  Otherwise it needs a hard-coded value.

Yes, it would be nice if you could indirectly specify the ID.  Post this request in the "We're Listening" (sometimes) section of the forum or send it directly to support@unitronics.com.

Joe T.

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Doesn't Visilogic support dynamic Slave ID? I was thinking I had a test program setup (once upon a time) where I could use entry keypad to set MODBUS slave ID, may have had to PTC the configure block in conjunction with new ID assignment. I recall it all working as expected. Everyone gets tired of hearing this from me (I'm quite sure), but here it goes again: "Why can't UniLogic have all the features of Visilogic and have all the new features of UniLogic"? A good share of Unistream sales (SURELY) is to Samba/Vision users who are upgrading hardware or at minimum very accustomed to Visilogic and it's feature set. It was a suprise to me as I slowly discovered the missing features. I know, I know... I want to have my cake and eat it to. Doesn't stop me from wishing :)

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