General Concepts of Script Development
Scripts can be developed in various elements of OPC server configuration: in nodes, devices, sub-devices or/and tags. While creating, a script includes 3 functions (for a tag) or 4 functions (for a node, device or sub-device): the initialization function, the deinitialization function, "before reading a device" function, and "after reading a device" function. A code is developed within bodies of those functions. User functions (see Function Definitions) must be declared out of system functions.
A script of a node, device or subdevice can include:
Global declarations (executed when loading a script)
Functions created automatically:
The initialization function (executed one time at node start):
function OnInit()
end
The deinitialization function (executed one time at node stop):
function OnClose()
end
The function executed before an attempt to read devices (executed periodically; a poll period can be set):
function OnBeforeReading()
end
The function executed after an attempt to read devices (executed periodically; a poll period can be set):
function OnAfterReading()
end
User-defined functions
A script of a tag can include:
Global declarations (executed when loading a script)
Functions created automatically:
The initialization function (executed one time at node start):
function OnInit()
end
The deinitialization function (executed one time at node stop):
function OnClose()
end
The function executed after reading a tag (created in the script after reading; executed periodically):
function OnRead()
end
The function executed before writing a tag (created in the script before writing; executed when attempting to write to a tag; the function is not executed when program writing):
function OnWrite()
end
The function is called by an OPC client when writing as well as while writing from a script of other tag. In order to detect that writing is performed from a script of other tag, the function server.IsWriteFromScript( ) is used.
User-defined functions