Start values not read in synchronously

Determines the initialisation behaviour for the first data request. The variable server normally reads the value synchronously from the communication interface the first time a process variable value is requested. This prevents incorrect accesses and incorrect data representations in the application, although in certain cases this can lead to errors or undesirable delays.

Setting	Description of the
	When a process variable value is requested for the first time, a read access is started. If this read access is asynchronous (according to the read access parameter of the definition group), the internal process variable cache of the variable server is not initialised until the asynchronous response is returned from the OPC server. Only then can the value be passed on to the visualisation. In this case, before the first values are returned from the communication component, incorrect 0 values are displayed in the control elements, for example.
	When a process variable value is requested for the first time, a synchronous read access is started, i.e. the variable server waits in the read call for the function execution of the communication component. This usually handles the synchronous call with a higher priority (directly after the currently running request), i.e. earlier. The returned value is returned to the visualisation client by the variable server directly after receipt. In certain cases, an error occurs when reading synchronously for the first time. This is characterised by the message `Item Read Error (<OPC-Server>):<process variable name>- 0x1` appearing in the VisiWin Manager immediately after the project is started. The reason for this phenomenon is that the internal initialisation of the OPC server is not yet complete. Other difficulties that can cause the initial synchronous reading are the relatively long loading times of views that contain a large number of process variable representations and the resulting seemingly complete standstill of the application down to the variable server (not only the visualisation interface stands still, but also other time-critical processes can no longer be carried out).

Setting

Description of the

When a process variable value is requested for the first time, a read access is started. If this read access is asynchronous (according to the read access parameter of the definition group), the internal process variable cache of the variable server is not initialised until the asynchronous response is returned from the OPC server. Only then can the value be passed on to the visualisation. In this case, before the first values are returned from the communication component, incorrect 0 values are displayed in the control elements, for example.

When a process variable value is requested for the first time, a synchronous read access is started, i.e. the variable server waits in the read call for the function execution of the communication component. This usually handles the synchronous call with a higher priority (directly after the currently running request), i.e. earlier. The returned value is returned to the visualisation client by the variable server directly after receipt.

In certain cases, an error occurs when reading synchronously for the first time. This is characterised by the message Item Read Error (<OPC-Server>):<process variable name>- 0x1 appearing in the VisiWin Manager immediately after the project is started. The reason for this phenomenon is that the internal initialisation of the OPC server is not yet complete.

Other difficulties that can cause the initial synchronous reading are the relatively long loading times of views that contain a large number of process variable representations and the resulting seemingly complete standstill of the application down to the variable server (not only the visualisation interface stands still, but also other time-critical processes can no longer be carried out).

Parameters for module: