Allen-Bradley: Read Node

The Allen-Bradley: Read Node allows you to read multiple tags from your Allen-Bradley CompactLogix or ControlLogix programmable logic controller (PLC) through EtherNet/IP. This node is only available in edge workflows.

Configuration

There are three main parts of the configuration for this node …

Address Configuration

Address Configuration contains three fields:

• Host: (Required) A string template for the IP address at which the PLC or EtherNet/IP Module resides.
• Slot: (Required) A string template or integer for the PLC Slot number.
• Keep-Alive Interval: (Optional) A string template or integer for the seconds between keep-alive connection requests. Set this value lower than your device’s connection timeout. Blank (the default) or 0 turns off the keep-alive request.

Read Instructions

You may define multiple read instructions for the Allen-Bradley: Read Node, and you must define at least one. Each instruction has the following fields:

• Controller or Program Tag: (Required) A string template.
• Program: (Optional) A string template for the program which your program tag is a member of. In case of a controller tag (above) leave this blank.
• Data Type: Atomic (SINT, INT, DINT, REAL, BOOL) or STRING. When giving read instructions via a payload path the only valid data types are ‘atomic’ or ‘string’.
• Result Key: (Required) The key at which to store the result of this read operation. This key will exist on the Destination Path defined below the instructions. This can resolve to any string except errors, since that key is reserved for any errors that occur during reads.

Destination Path

The results of each read instruction will be placed in an object at the Destination Path (a payload path) at each instruction’s Result Key. It is important that each key is named uniquely so the node does not overwrite another read result.

If the key is not present in the Destination Path of the payload, it means the read failed, and there will be a list of errors at the Destination Path under the key errors. For this reason, this node restricts Result Keys to not resolve to the path errors. Because the tags are read as a group one failed read for a tag may cause the other keys in the group to not appear.

Along with the Result Key and possible errors, each read object at the Destination Path will include a plcProperties object key. The PLC Properties object includes current device information about various possible faults, status, version, time, slot, serial number, and name.

The following is an example of a successful read, where an instruction’s Result Key is myProgramDint, and the Destination Path is destination.allenStart:

{
  "destination": {
    "allenStart": {
      "plcProperties": {
        "io_faulted": false,
        "majorUnrecoverableFault": false,
        "majorRecoverableFault": false,
        "minorUnrecoverableFault": false,
        "minorRecoverableFault": false,
        "faulted": false,
        "status": 12640,
        "version": "31.11",
        "time": null,
        "slot": 0,
        "serial_number": 1622838845,
        "name": "1769-L16ER/B LOGIX5316ER"
      },
      "myProgramDint": 42
    }
  }
}

The following is an example of a failure to read, where a resultKey should have been myProgramDint, and the destination path is destination.allenStart:

{
  "destination": {
    "allenStart": {
      "plcProperties": {
        "io_faulted": false,
        "majorUnrecoverableFault": false,
        "majorRecoverableFault": false,
        "minorUnrecoverableFault": false,
        "minorRecoverableFault": true,
        "faulted": true,
        "status": 12640,
        "version": "31.11",
        "time": null,
        "slot": 0,
        "serial_number": 1622838845,
        "name": "1769-L16ER/B LOGIX5316ER"
      },
      "errors": [
        {
          "type": "ALLEN-BRADLEY_READ_ERROR",
          "message": "Something useful to help you fix the issue."
        }
      ]
    }
  }
}