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Monitoring the IO Communications Status Using Status and IOStatus

By Julia Thompson,2014-06-23 21:02
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Monitoring the IO Communications Status Using Status and IOStatus

    Monitoring the I/O Communications Status Using Status and IOStatus All Tech Notes and KBCD documents and software are provided "as is" without warranty of any kind. See the Terms of Use for more information.

    Topic#: 000197

    Created: January 19, 1993

    Updated: June 28, 2001

    Summary

    InTouch? and the Wonderware?I/O Servers provide a way to monitor the communications status in an application. The IOStatus built-in topic (DDEStatus in FactorySuite? 1000 and the earlier versions of InTouch) can monitor the status of connection between InTouch and a data server. This connection can be between InTouch and Microsoft Excel, InTouch and an I/O Server, or two InTouch nodes in a networked application. Also, the Status bit in an I/O Server that was developed with the Wonderware I/O Server Toolkit? monitors the communication status between the I/O Server and the PLC. Once both bits are configured, they can flag you for trouble or provide a trigger for an immediate switchover to a standby PLC or computer. Status Item

    The Status bit is a built-in item available for each topic configured for the I/O Servers developed with the Wonderware I/O Server Toolkit. Example

    1. Suppose we have two DDE Topics defined in the I/O Server and two

    DDE Access Names, PLC1 and PLC2, which are defined as follows: DDE Access Name: PLC1 PLC2

    Application/Server Name: Modbus Modbus

    Topic: PLC1 PLC2

    2. We would then create two Discrete tags, PLC1Status and PLC2Status.

    o Each tag will monitor the status of the two conversations

    between the I/O Server and the PLCs.

    3. In WindowMaker, select Special/Tagname Dictionary and define the

    two tagnames as follows:

    Tagname: PLC1Status PLC2Status

    Type: I/O Discrete I/O Discrete

    DDE Access Name: PLC1 PLC2

    Item: Status Status

    o PLC1Status and PLC2Status will have a value of one when there

    is an active conversation between the DDE Topic in the I/O

    Server and the PLC.

    o Both will go to zero when the conversation is lost.

    Note: For the status bit of a topic to be valid, at least one item

    other than the status bit needs to be advised in the same topic.

    IOStatus Topic

    There is an IOStatus bit for each DDE Access Name that is defined in an InTouch application.

    Example

    1. Suppose we have three DDE Access Names that are defined as follows: Access Name: Master PLC1 Sheet1

    Node: Master Master

    Application Name: View Modbus Excel

    Topic Name: Tagname PLC1 [Book1]Sheet1

    o The Access Name Master is used to talk to InTouch on a computer

    with a node name of Master.

    o The Access Name PLC1 is used to talk to a Modbus I/O Server

    on a computer with a node name of Master.

    o The Access Name Sheet1 is used to locally talk to an Excel

    spreadsheet named Sheet1.xls on the same computer. Using this information, we can use the IOStatus bit to monitor the conversations set up by these Access Names by performing these steps:

    2. In WindowMaker, select Special/Configure/Access Names.

    3. Select New and define the IOStatus as follows:

    Access Name: IOStatus

    Node:

    Application Name: View

    Topic Name: IOStatus

    4. Create three Discrete tags in which each tag monitors the status

    of the three I/O conversations.

    5. In WindowMaker select Special/Tagname Dictionary and define three

    tagnames as follows:

    Tagname: Master_Status PLC1_Status Sheet1_Status

    Type: I/O Discrete I/O Discrete I/O Discrete

    DDE Access Name: IOStatus IOStatus IOStatus

    Item: Master PLC1 [Book1]Sheet1

    o The following diagram shows the relationship between the tags

    and Access names for the Modbus Access Name with the PLC1

    Topic.

    Note: The IOStatus will have a value of one when there is an active conversation between InTouch and the respective application and Topic that are being monitored. The tags will go to zero when the conversation is lost, or when there are no active items using the Application and Topic that are being monitored. Therefore, for IOStatus to be valid, at least one tag must use the Topic being monitored at all times.

    It is not recommended to use IOStatus as the only means to monitor the communications between InTouch and the I/O Server. Wonderware Tech Support strongly favors the use of a heartbeat (a timer or free-running

    counter on the remote View node or PLC) to monitor the communications (see related articles below for more details). The reason for that is that IOStatus uses the TCP stack built into Windows for communications, and it may take a few seconds for the stack to time out when there is no communications (the server is closed, there is a power failure, or the cable is disconnected). Or, it is also possible that the stack does not detect the communications failure and the IOStatus will not detect the condition either.

    Related Articles

    For more information and details about the use of a heartbeat to monitor communications between InTouch and the I/O Server, please read the following articles.

    ; Follow this link to Setting Up a "Heartbeat" Between Two InTouch

    Nodes.

    ; For an example of a hot backup strategy for PLCs using Status, see

    Configuring a "Hot Backup" Strategy for I/O Servers Using the Status

    Bit.

    ; For more information on configuring InTouch backup applications,

    see Configuring a "Hot Backup" Strategy for PLCs, I/O Servers, or

    InTouch Nodes.

    F. Gonzalez

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