Identifying and Changing an Unknown IP Address on the CP-2061

SW various 08.01.2026 07:53 08.01.2026 07:53

A PLC without an integrated display allows you to read and modify the ETH1 interface communication parameters using a USB flash drive.

Checking the Current ETH1 Settings

Procedure

  1. Turn off the supply to the PLC.

  2. Prepare a USB flash drive:

    • If the _PLC_RQCFG.JSON file exists in the root directory, delete it
      (or use a blank USB flash drive).

  3. Insert the flash drive into the USB Host connector on the PLC base module.

    • Supported file systems: FAT16, FAT32, exFAT, NTFS, ext4

    • Required free space: min. 1 MB

  4. Turn on the PLC and wait for the startup sequence to complete
    (see Section 6.1 of the TXV 004 50 documentation – Standard Startup Sequence)

  5. During startup, the PLC automatically saves the current ETH1 parameters to the file
    _PLC_RQCFG.JSON in the root directory of the USB flash drive.

  6. After the startup sequence is complete, turn off the PLC and remove the USB flash drive.

  7. Open the _PLC_RQCFG.JSON file on your computer.

Example content of the _PLC_RQCFG.JSON file

{
  "request": {
    "network": {
      "ETH1": {
        "dhcpEnabled": false,
        "ip": "192.168.134.176",
        "mask": "255.255.255.0",
        "gw": "",
        "dns1": "",
        "dns2": ""
      }
    },
    "userProg": {
      "rqClear": false
    },
    "webPass": {
      "rqClear": false
    },
    "modePlc": {
      "rqHalt": false
    }
  }
}

Changing the ETH1 Interface Settings

Editing the File

  1. Open the _PLC_RQCFG.JSON file and edit the desired ETH1 parameters.

  2. After editing, rename the file to PLC_RQCFG.JSON.

Example of Changing Network Parameters 

{
  "request": {
    "network": {
      "ETH1": {
        "dhcpEnabled": false,
        "ip": "192.168.134.176",
        "mask": "255.255.255.0",
        "gw": "192.168.134.1",
        "dns1": "8.8.8.8",
        "dns2": "1.1.1.1"
      }
    } 

Note on DHCP

If the following is set:

"dhcpEnabled": true

The PLC automatically obtains an IP address and other parameters from a DHCP server.
In this case, the values for ip, mask, gw, dns1, and dns2 are ignored.

Additional Options for the PLC_RQCFG.JSON File

The file can also be used to perform the following operations:

Deleting the user program

"userProg": {
  "rqClear": true
}

Deleting web configuration credentials

"webPass": {
  "rqClear": true
}

Setting the PLC to HALT mode after startup

"modePlc": {
  "rqHalt": true
}

Applying New Parameters to the PLC

Procedure

  1. Turn off the supply to the PLC.

  2. Insert the USB flash drive containing the PLC_RQCFG.JSON file into the USB Host port.

  3. Turn on the PLC and wait for the startup sequence to complete.

    • The PLC compares the new parameters with the current settings.

    • If a change occurs, the RUN and ERR LEDs will flash simultaneously
      (for approx. 10 seconds).

  4. After successful configuration:

    • PLC_RQCFG.JSON → _PLC_LAST_RQCFG.JSON (last command/request)

    • The PLC saves the current ETH1 status to the new _PLC_RQCFG.JSON

  5. Turn off the PLC and remove the USB flash drive.

  6. On the PC, you can compare:

    •  _PLC_LAST_RQCFG.JSON – requested changes

    • _PLC_RQCFG.JSON – current PLC status 

This procedure can be repeated as needed.

Checking the EVENT.LOG file

If the changes are applied successfully, entries such as the following will appear in the EVENT.LOG file:

PLC_RQCFG.JSON file has been activated
ETH1 modified: IP=192.168.134.176 IM=255.255.255.0 GW=192.168.134.1 DHCP=off

Important Notes

  • This feature is available only for PLCs without an integrated display

  • Required firmware: v7.5 and higher (released 10/2025)

  • The PLC_RQCFG.JSON file must be in JSON format (RFC 4627)

  • It is recommended to use the original _PLC_RQCFG.JSON file as a basis

  • If an invalid IP address is entered, the parameter changes will not be applied