Zero-based addressing and migrating from Wonderware MBTCP DAS Server to TOP Server

I have previously used the Wonderware Modbus TCP DAS Server for Modbus communications.  The server supports both zero and one-based addressing. We were using zero-based addressing which means we have addresses such as 300000 and 400000.

Now we are trying to use TOP Server but our 300000 and 400000 address references in the the Wonderware client are being returned as invalid by TOP Server. How can we access those addresses?

To use the same zero-based addresses you already have configured in Wonderware with TOP Server Modbus Ethernet, you will simply need to do the following:

1. Make sure there are no client applications currently connected to TOP Server (Client count in the bottom right corner of the TOP Server configuration must be 0).
2. Open the properties of your device in TOP Server.
3. Select the "Settings" tab.
4. Disable the setting labeled "Use zero based addressing".
5. Click "Apply".

This allows your 300000 and 400000 address references to work successfully with TOP Server.  The issue here is a difference in naming conventions being used between the two different servers.

Supporting details:

The Wonderware MBTCP DAS Server uses the term "zero-based" to indicate that the first Modbus offset, which is 0, corresponds to the address 400000 and Modbus offset 1 corresponds to 400001 for holding registers, and so on.

TOP Server, however, uses the term "zero-based" to indicate that the #1 register, holding register 400001 for instance, will request Modbus offset 0, and 400002 will request Modbus offset 1, and so on.  The reference to zero-based or one-based in TOP Server is specific to the offset that will be requested by the address #1 register for the register type instead of referring to whether the starting register number is 0 or 1.  This is the methodology as it is referenced in the Modbus protocol specification, which is why it is used in TOP Server.