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Unitronics Vision Modbus floats

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Hi all.

I am trying to configure VTS Trihedral Scada system with a V120 PLC configured as slave, for monitoring a lift station using Modbus protocol. I can read/write from VTS to registers MBs and MIs, however am having a hard time with the floats (MFs registers).

According with Unitronics Modbus Slave Table, the Modbus register for MF 0 starts at 7700. I am trying to read MF 20 and I've tried in VTS 47721, 37721, 407721, and 307721 with no results; the VTS Modbus driver does not seem to understand this addressing and simply draws a blank. What am I missing?

I've googled and tried researching this issue but have not found much on Unitronics Modbus floats.

Any help would be greatly appreciated.


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Thanks, for your reply,

Yes, I tried that too, but it does not work either. Modbus starts counting on 1 not 0, so generally you have to add 1,

By reading deeply in the Unitronics help found that I have to add xx/FLOAT to the address, so I was able to bring at least a number that changes by using 7741/FLOAT. The 41 is because a read a post in the forum where somebady was able to read ML registers in Modbus by using (MLx2+1)+45100 (5100 is for MLs), thus applied same formula for MF plus the \FLOAT.

However I am reading in VTS a very low ridiculous number that changes, when I change it in the MF Unitronics register. I have the feeling that what am reading is the two 16 registers that makes the float in reverse order, and have to find a way to swap them.

Thanks again.

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  • MVP 2014

If you needed to swap the bytes in the PLC, as far as I can see you can do it in two steps:

1. Use the "Vector" -> "Struct" block to take the MF bytes and copy to a DW. This copies the bytes as they are, instead of interpreting them as a number

2. Use the "Vector" -> "Swap Bytes" Function and use the "32-bit" option to swap the upper and lower words of the DW value.

To read the value via SCADA you have two options

  • Use the SCADA "read float" function, but point it to the address of the DW in the PLC


  • Use the "Vector" -> "Struct" block again to copy the bytes of the new modified float back into an MF register (note this will show a strange number when viewed as a float in Visilogic, becuase the words have been swapped). Then point the SCADA function to the MF register.

I hope this helps.

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