What protocoI does Freelance/DIGIVIS use to communicate with AC800F?
I am aware that there might be multiple ways to get variables accross differente PLCs/devices. One way is to create an OPC server in freelance and get the variables from AC800F to Labview. Another method can be via modbus.
1. I have an FI820F. Is is possible that I can transmit my variables defined in freelance to Labview using FI820F modbus?
2. Physically the connection with the engineering station and AC800F is ethernet. What protocol is used between freelance/digivis with ac800f? Can I use this protocol to get variable data from AC800F in labview?
As per your second question: It's DMS (Digimatik message specification), a subset of MMS (ISO 9506). You can look up the details in the Freelance open couplings manual about DMS/API.
As I'm not familiar with LabView, your questions probably largely depend on what exactly LabView is able to understand. Freelance speaks multiple field buses (MODBUS/RTU is only one of them), but you can also use "pure" Ethernet transfer on the system bus using special function blocks, or a custom serial protocol, or OPC. My intuition suggests the latter might be the least painful way.
As per your first Question: FI820F can be Modbus Master or Modbus slave, so in principal it should work. Just remember that Modbus knows only Coils (Boolean) and Registers (16 Bit values). If you want to transport a floating point value from Freelance to Labview you need to split it into 2 x 16 Bits and transport it via 2 registers. Freelance offers a function block RTOME (Real to mantissa, exponent) in the Modbus Master block library that does exactly that. Question is, whether Labview can combine those two Registers to re-build the original floating point value. Freelance also offers the inverse conversion METOR in the same block library. That way you can get floating point values from Labview.
Please note that while those function blocks are in the Modbus Master library they can also be used by a Modbus Slave configuration.
There is programming interface called DMSAPI that can be used by customer applications on Windows systems to access values in the same way DigiVis or the OPC server do. (C language API)
You would integrate DMSAPI.DLL into your Labview application. Probably a kind of wrapper is needed. Then you add it as DMSAPI-Gateway to the Freelance-Project.
After this you can download the configuration required to access values on the controller to your Labview application.