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Reading strings from modbus slaves result with wrong text


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I now have a few unitronics PLC's on site, I am getting more familiar with them but still fairly new.

I have an application where the PLC talks to a cobot over modbus, everthing works great, never had any problems with it. This morning i was asked if I could display the "current program" running on the cobot on the unitronics HMI. 


I thought it would be as easy as just reading a string data type.. 

I'm now thinking that to read the string, I read each interger in addresses 7701-7799 assuming that the numbers are Ascii code(manual doesnt say) then concatenate them to get the string.

Does anyone have experience of reading strings from modbus slaves??

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  • 3 weeks later...

I spoke to soon on this one. I thought it was working but I just didnt look at the result properly.

Each pair of letters in the string are switched.

So the cobot has a program in it called "320rpm" reading this over modbus (as above) and displaying the result on the HMI I get "23r0mp"

Anyone have any ideas on how to fix this one?


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  • MVP 2023

As a Vision only user, that looks like an Endian problem, which would require some simple rearranging of data, in a consistent pattern for everything received. 

In Vision this is done with Swap Bytes, don't know what it is called in Unilogic, but have to assume it exists.

cheers, Aus

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  • NoamM changed the title to Reading strings from modbus slaves result with wrong text

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