Modbus Agent Tab

To create a Modbus source system, do the following:

  1. Create a source system of the type Modbus source system.

  2. Make the following settings on the Modbus Agent tab:

    Field

    Description

    Modbus Client

    The Modbus type Modbus client defines that PCo is the leading system. PCo can send queries to the connected devices. In this case, the devices act as servers.

    Modbus Server

    The Modbus type Modbus server defines that PCo is the subordinate system. PCo can receive queries from the connected devices. In this case, the devices act as clients.

    Acceptable Quality

    With this setting, you define the permitted data quality of the tags. When a tag is read out of the Modbus source system, the data quality of the tag is also provided and can be taken into account accordingly.

    The following data quality settings are possible:

    • Any Quality

      This setting means that the data quality of a tag is not taken into account and all tag values are accepted.

    • Good

      This is the default setting. If you choose the Good setting, only tags with good data quality are used. If the data quality is poorer (Uncertain, Bad, Error), PCo issues an error message.

    • Uncertain

      If you choose the Uncertain setting, only tags with the data quality Good or Uncertain are accepted. The status Uncertain is set if the Modbus server does not respond.

    • Bad

      If you choose the Bad setting, PCo also accepts tags with poor data quality. The Modbus server sets the data quality of a tag to Bad if a tag cannot be read.

    • Error

      The Modbus server sets the data quality of a tag to Error if the call has failed. The effect of the Error setting is that tags with incorrect data quality are also accepted by PCo.

    Channel

    You choose the communication channel here:

    • TCP

    • Serial communication

    Response Timeout

    Indicates the period in which the connected Modbus device must send a response. If the specified time is exceeded, an error message is issued. The default setting is 200 milliseconds.

    Minimum Update Rate

    Specifies the minimum time for the update rate in milliseconds (ms).

    • Specifies how often the data is to be read by the connected device

    • Specifies the minimum time that has to be passed before the Modbus source system sends the next value change to PCo. If you enter 100 ms, at least 100 ms need to have passed between the sending of two messages.

  3. Make the settings for TCP or for serial communication: