RS-485: Imported from Wikipedia (overwrite)

2026-05-03T13:59:49Z

Imported from Wikipedia (overwrite)

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{{Short description|Group of client–server standards}}
{{more citations needed|date=July 2016}}
{{Infobox protocol|name=OPC Data Access (OPC DA)|image=|industry=[[Operational technology]] and [[Information technology]]|standard=OPC DA specification|developer=[[OPC Foundation]]|introdate={{Start date and age|1996|08}}|homepage=https://opcfoundation.org/about/opc-technologies/opc-classic/|newer=[[OPC Unified Architecture]]|hardware=[[Windows]]}}
The '''OPC Data Access''' Specification is the first of a group of [[Specification (technical standard)|specifications]] known as the [[OLE for process control|OPC]] Classic Specifications.<ref>{{Cite web|url=https://opcfoundation.org/developer-tools/specifications-classic/data-access/|title = Members}}</ref>

OPC Data Access is a group of [[client–server model|client–server]] standards that provides specifications for communicating real-time data from [[data acquisition]] devices such as [[programmable logic controller|PLC]]s to display and interface devices like [[human–machine interface|Human–Machine Interfaces]] (HMI), [[SCADA]] systems<ref>{{Cite web|url=https://opcfoundation.org/about/what-is-opc/|title = What is OPC?}}</ref> and also [[Enterprise resource planning|ERP]]/[[Manufacturing execution system|MES]] systems.<ref>{{Cite book | url=https://books.google.com/books?id=8Lj8CAAAQBAJ&q=ERP%2FMES%20%22OPC%20DA%22%20OR%20%22OPC%20Data%20Access%22&pg=PA352 |title = Fieldbus Technology: Industrial Network Standards for Real-Time Distributed Control|isbn = 9783662072196|last1 = Mahalik|first1 = Nitaigour P.|date = 2013-03-09| publisher=Springer }}</ref> The specifications focus on the continuous communication of data.

The OPC Data Access specification is also known as OPC DA. OPC DA deals only with real-time data and not historical data (for historical data you need to use [[OPC Historical Data Access]], or OPC HDA) or events (for Alarms and Events you need to use [[OPC Alarms and Events]], or OPC AE). There are three attributes associated with OPC DA data. These are
# a value,
# the [[quality (business)|quality]] of the value, and
# a [[timestamp]].

The OPC DA specification states that these three attributes have to be returned to an OPC client making a request. Therefore, if the data source is not capable of providing a timestamp, for example, the OPC DA server must create a timestamp.

The OPC Classic specifications are based on the [[Microsoft]] [[Component Object Model|COM]] technology<ref>{{Cite web|url=https://opcfoundation.org/about/opc-technologies/opc-classic/|title = Classic}}</ref> and define a [[C language|C]]/[[C++]] [[Interface (computing)|interface]]. A standard [[OLE Automation|Automation]] [[Wrapper library|wrapper]] interface is also defined for access from [[Visual Basic]], [[Embarcadero Delphi|Delphi]] and other automation-enabled languages.<ref>{{Cite web|url=https://opcfoundation.org/developer-tools/developer-kits-classic/automation-wrapper/|title=Members}}</ref> Several vendors offer [[.NET Framework|.NET]] toolkits to make the OPC interface accessible in .NET [[Application software|applications]].

The newer OPC .NET ([[OPC Xi]]) specification is based on WCF ([[Windows Communication Foundation]]) and defines a .NET interface with the functionality of the OPC Classic specifications OPC DA, OPC HDA and OPC AE (Alarms&Events).<ref>{{cite web |url=https://opcfoundation.org/about/opc-technologies/opc-net-4-0/ |title=.NET 4.0 (WCF) {{!}} OPC Foundation |website=opcfoundation.org |url-status=dead |archive-url=https://web.archive.org/web/20140703074027/https://opcfoundation.org/about/opc-technologies/opc-net-4-0/ |archive-date=2014-07-03}} </ref>

The more recent [[OPC Unified Architecture]] allows the same functionality but offers platform independence and optionally complex information modelling capabilities.<ref>{{Cite web|url=https://opcfoundation.org/about/opc-technologies/opc-ua/|title = Unified Architecture}}</ref>

==See also==
* [[OPC Foundation]]
* [[Distributed Component Object Model]]
* [[OPC Unified Architecture]]

==References==
{{Reflist}}

==External links==
*[http://www.opcconnect.com/ OPC Programmers' Connection]

{{Automation protocols}}

{{DEFAULTSORT:Opc Data Access}}
[[Category:Industrial automation]]

OPC Data Access - Revision history

RS-485: Imported from Wikipedia (overwrite)