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first of all I want to apologize in advance if it is not post in the right place or if my English is not good, I try to do my best.


good now I explain my problem, as part of a school project, I have to adapt two PLC to control mini industrial facilities. that's good every automaton controls his installation


only now I have to communicate two automata between them to be able to control stations from different automata so for that I use the block (RIR # 4) and it works perfectly for my first 4 values (here as can be seen on the programs reconstituted, since the master, we read the 4 word from the word 46 and we stocks from the word 200.


the problem comes after, when I have to transfer a simple status bit (0 or 1 so). I use the bit to num function to put it in the form of a word, I try to read that word, and I use num to bit to recover the bit that interests me, but it does not work 

so I did a test, and it turns out that the bit is well transformed into a word, but that the RIR block # 4 does not read this word, while yet it seems to configure well. in summary, I try to transform my MB40 bit in the word MI100, and it seems to work, it's when I try to read my MI100 word to put it in MI240 that it seems to be wrong because when I try to display MI240 it remains at 0.

I leave you as an attachment a reconstruction of the part that seems cloche of my program (the master and the slave, my teacher not wanting me to diffuse the programs of a school project)



I really hope you can help me, thank you very much

(PS: my PLCs are V350-35-TRA22 and a V350-35-TR20)


master 1.vlp slave 1.vlp

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  • MVP 2023

First of all, you need to Read Holding Registers (R.H.R #3), not Read Input Registers (R.I.R #4).

Also, you can read and write bits (coils) directly using Read Coils #1 and Force Coils #5 or #15.

But the simplest method when you are communicating between two Unitronics Vision PLCs is to use the FB Read/Write Mixed Data. This FB allows you to enter a mix of operands and read or write them directly using a single function call.

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  • MVP 2023

Also, do NOT use SB 3 for your communications. If one second intervals are sufficient for your communications, use SB 13. SB 3 will cause the PLC to attempt comms on every PLC scan for fully half of each second. You want to trigger communications with a transition contact or SB 13, which is automatically a transition contact.

And place an inverted contact of MB 100 in front of the comms FB.

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