Technical Reference > CtAPI Functions > Reading Data Using the CTAPI Functions > I/O tags interface

I/O tags interface

The CitectSCADA I/O Server is designed on a client read on demand basis. The CitectSCADA I/O Server will read I/O tags from the I/O Devices when requested to by a Client. This reduces the load on the I/O Devices and increases the overall system performance.

The client interface to the real time data is more complex as the client needs to wait for a physical I/O cycle to complete before the data can be used. The client needs to request the data it requires from the I/O Server and then wait up to several seconds while the I/O Server reads the requested data. This design is reflected in the operation of the CTAPI interface. Using CTAPI to read a tag can take several seconds to complete. It is up the caller to allow for this in their design in calling this interface.

If you need to use a polling type of service, use the ctList functions.

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