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Hi, I'm having hard time displaying data that I get through MODBUS. Need to read from multiple slaves, but after download display still shows 0. Maybe do I need to write data to data table and then display on HMI? Or I can just display data vector? I'm really confused, thanks in advance for your help. 

P.S. Program attached below.


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  • MVP 2023

Yes, you can display your MI read from the slave directly on the HMI screen. If it's just displaying zero, then you should confirm that you are in communication with the slave. Are you getting increments for Status Messages, Sessions, and Acknowledgements? Are you certain you're reading the right register addresses? Are you sure the slave registers have a value other than zero?

One other thing, you only need one COM INIT block unless you are wanting to change your COM properties on the fly.

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Hi Justas;

I have looked  at your program.

You appear to be using the USB port for programming and   COM 1 for Modbus, You cannot do this .

The USB port is probably set for 115,200 and the Modbus is set for 9600

The Installation manual says :

The USB port may be used for programming, OS download, and PC access.

Note that COM port 1 function is suspended when this port is physically connected to a PC.


. Add a 2nd Com Port to the PLC  V100-17-RS4X


 Setup the Ethernet port and program thru the Ethernet Port - nice feature in the V700. --  see below


You Initialize the Modbus  several times - 1 for each device.

This Modbus Config is for this unit- the Master(Client)  This is Modbus ID 1 - only need to do this once.

You have to set up each device to a different Modbus Address.   ID address 2 , etc.

In the Modbus  Read Holding registers, this is where you define the Server(Slave) address to read from.-


Trim the program to work with 1  Modbus Slave  unit to start, and get it working, then add the others in.


Typical Ethernet Setup Line:


--||-------PLC Name ----- TCP/IP Config   ------  TCP Socket Init

SB2 - Power up                  Set the IP address        Socket 1, Port 20256, TCP,Slave

In the   Connectons, change Serial to Ethernet, and then favorite, and enter the PLC name, IP Address, and  port 20256.

Be sure the IP address is on the same network your PC is on, and is an unused IP.  After setting up the PLC, do a PING from the

PC to  be sure you can see the PLC.






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