PLC-5: unsolicited messages on a DH+ network

An unsolicited message is generated in a PLC-5 by programming a Message Instruction. Refer to the PLC-5 Instruction Set Reference for help on how this instruction is programmed. The Message instruction requires several fields to be programmed properly for it to function properly. These fields are as follows:
  1. Set up the message instruction. The message instruction requires several fields to be properly programmed. For a PLC-5, these fields are as follows:
    • Communication Command = PLC-5 Typed Write
    • PLC-5 Data Table Address = the starting address of the data to be sent from in the PLC
    • Size In Elements = the amount of data to be transferred
    • Local/Remote = Local (Remote Station, Link ID, and Remote Link Type = N/A)
    • Local Node Address = the address of the RSLinx Classic driver receiving the MSG
    • Destination D.T. Address = the address where clients connecting to RSLinx Classic receive incoming data
    • Port Number = the communication channel out of which the data will be sent out
  2. Receive the message in the client via DDE.
    1. In RSLinx Classic, configure a DDE topic to the PLC sending the data. Ensure the Data Collection mode is set to Unsolicited only.
    2. If using DDE, create a hotlink (Automatic Link in VB) to the address that will receive the data (Destination D.T. Address from the MSG).
    3. When the hotlink is established, the data value is 0 until a data message is received. RSLinx Classic automatically sends the message to the client once the hotlink is established and the MSG is received.
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