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When Simulate Device is enabled in TOP Server, both clients must have the same update rate in order for a value written by one client to be read by another.

When a Client Writes to a Device That Is In Simulate Device Mode, Other Clients Cannot Read the Value.

The purpose of this FAQ is to explain how Simulate Mode works in TOP Server and how it can used to see changing data. This information applies to all versions of TOP Server.

1. Simulate Mode with OPC Clients

It is a common misconception that Simulate Mode allows the simulation of a device as is done with a soft PLC. This is incorrect. Simulate Mode is intended to be used when no physical device is available, but it is necessary to make sure a client application is functioning properly. It essentially echoes back to the connected client application anything the client writes to each tag. If nothing has been written to a Boolean or Analog tag, the value echoed back to the client is zero. If nothing has been written to a String tag, the value echoed back is a null character (the string display is blank).

1.1 Why Can’t Two Clients See the Same Data

The server creates poll groups based on the update rates configured in an OPC client application. When the server is placed in Simulate Mode, it is these poll groups that are echoed back to the client. If two clients use different update rates, different data values are echoed back even when the clients are addressing the same tags. To use one OPC client to change data in the server and see it with another, connect both clients using the same update rates.

2. Simulate Mode with Non-OPC Clients

Tag update rates are not specified from within non-OPC clients. The Scan Rate of each tag is set within the server. When using Simulate Mode with non-OPC clients tag values are still echoed back to the client application. A non-OPC client connected to the same items sees changes made from another non-OPC client.

3. Simulate Mode with OPC and Non-OPC Clients

If using a non-OPC client to simulate changing data using the OPC Quick Client, ensure that the Update Rate used in the Quick Client is the same as the rate used for the client. There may also be an option of using the Alias Map feature to perform an override of a tag Scan Rate.
If your non-OPC client is already requesting values based on the Tag-Specified scan rate, you can change the Scan Mode in the Device Properties to match this behavior.