Configuring Communications for the MSG Instruction

Use the MSG instruction to:
  • program a block transfer between the controller and a Remote I/O (RIO) block transfer module. A named RIO module entry (RIO-MODULE) must exist in the Controller Organizer I/O Configuration module tree in order for block transfers to occur.
  • send a broadcast message to a receiving controller using the controller's serial port.
  • enable large connection support for messages (if the target module supports large packets).
NOTE: Logix Designer versions 37 and later do not support controllers with serial ports. The
Broadcast
 button appears only in Logix Designer versions 36 and earlier for controllers with a serial port.
To configure communications:
  1. Do one of the following:
    • Select the
      Path
      button to specify a path.
      In the Path field, type the path or click the
      Browse
       button to find the desired module in the module tree.
      TIP: The module must have a name to be the target of block transfers.
    • Select the
      Broadcast
       button to send a broadcast message, and then select the channel used to send the message.
      The message path is set to 2,255 for channel 0 or 3,255 for channel 1.
      TIP: This option is enabled only when you choose a compatible system protocol and a write message type.
  2. Select the Communication Method for the message. Choose whether the message is routed via CIP,
    DH+
     link, or CIP with Source ID.
    TIP: Broadcast messages only support the CIP communication method.
  3. Check/clear the Connected box to indicate whether the message is to be sent Connected or Unconnected. This field is enabled only for CIP Generic messages except when the
    Broadcast
     button is selected. Broadcast messages only support unconnected messages.
    TIP: If the target device does not support connected CIP messages and this box is checked, an error appears when the message instruction is executed.
  4. Check or clear the
    Cache Connections
     option.
    • If this option is checked, the controller keeps the connection open after it completes the block transfer.
      The next block transfer uses the open connection and avoids the delay required to open the connection.
    • If this option is cleared, the controller closes the connection after the block transfer operation is complete.
      Selecting the option results in faster block transfers, but indefinitely retains a connection. Since the controller has a limited number of connections, this could eventually result in the controller being unable to establish connections.
  5. Select the
    Large Connections
     box to allow the CIP Generic type messages to use a large connection size (4002 bytes) for message transmissions. This check box is enabled only when the
    Connected
     box is selected, and CIP Generic is selected as the message type on the
    Configuration
     tab.
    TIP: Not all service types under the CIP Generic message type support Large Connections. Before selecting a large connection, make sure the device (determined by the communication path), service, class, instance and attribute support this feature. If you select an invalid service type, an error message displays.
  6. Select
    OK
    .
Accessing the Message Configuration dialog box, Communications tab
To access the Message Configuration dialog box, click the Tag Editor to make it the active window, and then click the button to the right of the MESSAGE operand. From the
Message Configuration
 dialog box, select the
Communications
 tab.
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