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How LabVIEW Uses I/O ServersPublish Date: Sep 07, 2012

Overview

An I/O server is a Shared Variable Engine (SVE) Plug-in that enables communication with devices and applications that do notuse National Instruments proprietary NI Publish-Subscribe Protocol (NI-PSP) utilized by Shared Variables. I/O servers are thebridging elements between shared variables in a LabVIEW VI and data tags in OPC, Modbus, or EPICS. I/O servers plug into theSVE to provide a list of items available for subscription and to provide that data to the SVE. With the LabVIEW Datalogging andSupervisory Control (DSC) Module, you can create in LabVIEW I/O servers to communicate with OPC, Modbus, and EPICSclients. This document will cover these three types of I/O Servers.

Table of Contents

Table of Contents

OPC ClientsModbusEPICS ProtocolRelated Links

OPC Clients

The provides OPC Client I/O servers for communicating with anyLabVIEW Datalogging and Supervisory Control (DSC) Moduleserver implementing the OPC Foundation OPC-DA protocol, which is a Microsoft COM-based standard. An OPC Client I/O serverlists all OPC servers installed on the computer and makes accessible groups and items on the server. You can create an OPCClient I/O server to access data items on a local or remote OPC server.

Figure 1: LabIVEW and OPC Network with DSCOPC Client I/O Servers allow for the Shared Variable Engine to bind the OPC tags from an OPC Server to Shared Variables.These bound Shared Variables provide an easy to use way for LabVIEW to read and write data to the OPC Tags. OPC Serversare separate pieces of software outside of LabVIEW, and National Instruments provides the as a separateNI OPC Serverpurchase.Modbus

Modbus is an application-level messaging protocol that provides master/slave communication between devices connected ondifferent types of buses or networks. You can create a Modbus or Modbus Slave I/O server to read data from or write data toModbus devices. For example, you can create a Modbus Slave I/O server on a National Instruments Real-Time controller and usethis controller as a Modbus slave device. You also can create a Modbus I/O server on a host computer and use this server as aModbus master device to communicate with a Modbus slave device.

Figure 2: LabVIEW and Modbus NetworkThe and the provide the Modbus I/OLabVIEW Datalogging Supervisory Control (DSC) Module LabVIEW Real-Time ModuleServers that plug into the Shared Variable Engine. The I/O Servers handle the low level protocol needed for establishingconnections and transmitting data between a master and slave. The Shared Variable Engine binds the data from the I/O Serversto Shared Variables that LabVIEW can easily read and write to. No additional software purchase is needed to connect LabVIEW toa Modbus device.EPICS Protocol

The Experimental Physics and Industrial Control System (EPICS) is a set of open-source software tools you can use to developlarge, distributed control systems. EPICS also refers to the architecture of such systems, as well as to the collaboration group

developing the related tools. Refer to the for more information about EPICS and toArgonne National Laboratory web site

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developing the related tools. Refer to the for more information about EPICS and toArgonne National Laboratory web sitedownload the latest version of EPICS. EPICS systems use the Channel Access (CA) network protocol to pass data betweenChannel Access clients (CACs) and Channel Access servers (CASs). The CA network protocol is a TCP/IP-based protocol.

Figure 3: EPICS Channel Access NetworkLabVIEW Datalogging and Supervisory Control (DSC) Module and the act as Channel Access (CA)LabVIEW Real-Time Moduleclients through I/O servers. The EPICS I/O servers are also available for for free on National Instruments website. Usedownloadthe EPICS Client I/O servers to monitor and update process variables (PVs) that an input/output controller (IOC) or ChannelAccess server (CAS) publishes using the CA network protocol. With EPICS Server I/O servers, LabVIEW acts as a server thatuses the Channel Access (CA) network protocol. Use EPICS Server I/O servers to publish shared variables by using the CAnetwork protocol. An EPICS Server I/O server is a Channel Access server (CAS). You can create an EPICS Server I/O server topublish local and remote shared variables and CompactRIO I/O variables (IOVs).Related Links

Developer Zone: Introduction to OPCDeveloper Zone: Connect LabVIEW to Any PLC Using OPCDeveloper Zone: Introduction to ModbusDeveloper Zone: Connect LabVIEW to Any PLC Using ModbusDeveloper Zone: Introduction to EPICSDeveloper Zone: Interactively Configuring EPICS I/O Servers