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Hello friends, I am having trouble developing the program for rs485 communication with a danfoss inverter and a softstarter weg ssw07. I am doing a logic of SET and RESET, after communicating with a condition equipment to the next and at the end RESET both. However it is presenting a number 4 and 5 fault. Someone would have a program that could serve as an example for me where I can communicate with several slave, automatically forming a loop cycle.

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  • MVP 2023

You need to separate your networks.  You have several networks that have multiple rungs, each of which is a logical statement.  There's no memory cost for additional nets- move your logic into pieces.

You also have rungs that initialize values, such as Main:Net 3 where you write 50 to SI 104.  It's better practice to use the power-up value feature for all of this-


This applies to SB 168 and SI 108 as well.

In net 2, don't put conditions on the SCAN block.  Just put a NC of SB 2 on the rail and hang it from that.

I would start by talking to one device at a time first and getting that working.  Then we can switch between them.  We need to solve the Modbus going to 4 and 5.

RS485 can be tricky on the older models such as the V230.  You may have to play with moving the terminator resistors around or eliminating them.  Make sure you have your RS485 polarity right, too. 

Even though the official Unitronics documentation shows a terminator at both ends, on these old models I have looked at the signal with a scope and found the terminators attenuate the signal too much.  Try removing one or both of the terminators while you're trying to get successful communication.

Joe T.


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