When RSLinx Classic or FactoryTalk Linx cannot see a PLC, check five things: which communication software is in use, the driver and its discovery method, the USB link, RSLinx Classic itself (service, activation, DCOM), and the shortcut in the FactoryTalk application. This article uses only two public Rockwell Automation guides, LINX-GR001Z for RSLinx Classic and LNXENT-GR001Z for FactoryTalk Linx. They are getting-results guides, not troubleshooting manuals, so anything they do not state is left out.
1. Find out which software is connecting
- Studio 5000 Logix Designer V31 and later can use either RSLinx Classic or FactoryTalk Linx for browsing and going online; the default is RSLinx Classic. Choose under "Communications > Select Communication Software...", after closing open projects (LNXENT-GR001Z p. 56).
- In ControlFLASH, use "Change RSLinx Edition". RSLinx Classic covers DH+, DF1, DH485, ControlNet, DeviceNet, EtherNet/IP and USB; FactoryTalk Linx covers USB and EtherNet/IP only (LNXENT-GR001Z p. 56; LINX-GR001Z p. 59).
- FactoryTalk Linx gives FactoryTalk View SE and ME access to Logix tags through shortcuts (LNXENT-GR001Z p. 100). RSLinx Classic is an OPC and DDE server for clients such as FactoryTalk View SE (LINX-GR001Z pp. 9–10).
If one package sees the PLC and the other does not, check this first. FactoryTalk Linx does not communicate with Remote I/O or with the earlier 1771, 1747, 1794 and 1797 backplanes (LNXENT-GR001Z pp. 51, 53).
2. RSLinx Classic: drivers and RSWho
Add a driver under "Communications > Configure Drivers": pick it in "Available Driver Types", click "Add New", name it (up to 15 characters), enter the parameters and click OK. It then appears in "Configured Drivers" (LINX-GR001Z pp. 14, 59–60). The guide has no table of which driver suits which network; it points to "Help > Quick Start" and the "What is a driver?" help topic (pp. 14, 38).
When RSWho shows no devices (LINX-GR001Z p. 24):
- "Autobrowse" is selected by default. If it has been cleared, "Refresh" runs only one discovery cycle and may need several clicks.
- A red X means RSWho recognised the device before but cannot reach it now, for example because it was unplugged. Right-click > "Remove" clears it from the display.
- Right-click a device for "Station Diagnostics"; "Communications > Driver Diagnostics" shows each driver (p. 18).
For USB, the USB CIP driver appears in Configure Drivers as the "Virtual Backplane (SoftLogix58xx, USB driver)" type. It can be installed manually from the RSLinx Classic installation directory: \Redist\USBCIP_3.18.06 for 32-bit Windows, or the x64 package \Redist\KN64Bit_2.01.01 for 64-bit (LINX-GR001Z p. 55).
3. RSLinx Classic does not run, or runs as the wrong edition
RSLinx Classic runs as a service by default. To change its configuration it must run as an application: in "RSLinx Classic Launch Control Panel", click "Stop", clear "Always Run As Service", click "Start" (LINX-GR001Z p. 22).
Safety: stopping the RSLinx service stops all communication through it (p. 22), and changing FactoryTalk Linx configuration at run time can cause unexpected results (LNXENT-GR001Z p. 41). On a running plant, follow the site's permit-to-work rules.
The "Troubleshooting installation" section (LINX-GR001Z p. 22) lists four checks: at least 512 MB of RAM; at least 2.2 GB of free disk space; the correct activation (if RSLinx shows as Lite, Single Node or OEM, the guide says the proper activation files were not installed); and whether an earlier Service Pack was reinstalled or a component such as DCOM removed.
The edition shows in the title bar. Lite has no OPC or DDE; Single Node serves OPC and DDE to one device only; OEM to any number of devices (pp. 9–10). Without activation files RSLinx runs as Lite (p. 9), and it also starts as Lite when the seven-day grace period ends (p. 43). An OPC client such as FactoryTalk View SE then gets no data through it.
DCOM: after the Microsoft KB5004442 patch, Rockwell software uses Packet Integrity as its minimum DCOM authentication level, and OPC DA communication between computers at different levels fails. Rockwell recommends updating the software on every computer; the DCOMAuthLevel utility adjusts the level (LINX-GR001Z pp. 11–13; LNXENT-GR001Z pp. 25–26).
4. FactoryTalk Linx: the Ethernet driver and discovery
Drivers are added in FactoryTalk Administration Console or in the stand-alone Network Browser, under "Rockwell Software > FactoryTalk Linx > FactoryTalk Linx Browser" (LNXENT-GR001Z pp. 45, 80).
| Discovery method | How it works | Notes |
|---|---|---|
| Local Broadcast | UDP broadcast to the computer's own subnet | Default for new drivers; switches can block broadcasts; with a specific network card selected, only that card is used (p. 48) |
| Remote Broadcast | Broadcast to another subnet; enter "IP Address" and "Subnet Mask" | Switches can block it, so nothing is found; then use Device List/Range (pp. 48, 69) |
| Device List/Range | Queries each IP address, range or DNS name directly | Up to 255 items; ranges with many unused addresses create ARP traffic that can make a device stop communicating; a badly formatted item gets a red outline and is ignored (pp. 48–49, 70) |
- Advanced tab, "Use “Windows Default” when selected interface fails": when enabled and the selected network card is lost, FactoryTalk Linx moves to another card and may talk to a device with the same address on the other network (pp. 72–73).
- A red X in the Network Browser means the device can no longer be recognised, for example after a cable was pulled (p. 49).
- Some EtherNet/IP devices do not support the FactoryTalk Linx browse protocol: right-click the network > "Add Device", after registering the device with the Device Description File Installation Tool (pp. 80, 84).
5. The USB connection does not come up
From "Troubleshooting USB Component" (LNXENT-GR001Z pp. 76–79):
- In Device Manager, a plugged-in USB CIP device should appear under "Rockwell Automation USB CIP Devices"; open Properties and read "Device status".
- A device shown only in the virtual backplane as an "Unrecognized Device" with a yellow question mark has no registered HardwareDatabase.xml file (p. 77).
- Rule out the device, cable and port: try a computer known to work with similar devices, another cable and another USB port.
- Check in Task Manager that the USB CIP Helper service is running. It assigns virtual backplane slots from slot 16 downwards and warns when no slot is free or slots conflict.
For Logix controllers, the guide advises using USB for program upload and download, monitoring, ControlFLASH updates or a temporary Studio 5000 connection, not for reading or writing tag data (p. 78).
6. FactoryTalk Linx shortcuts for FactoryTalk View
- Each device the application needs must have a shortcut, stored per FactoryTalk application (LNXENT-GR001Z p. 85).
- In Communication Setup, click "Add", select the device in the tree, click "Apply". Shortcuts are saved only when you click OK to close Communication Setup; "Verify" shows each shortcut's status (pp. 85–86).
- A shortcut with the same name as an RSLinx Classic topic hides the tags of one of them in a tag browse (p. 86).
- FactoryTalk Administration Console cannot browse tags; use FactoryTalk View Studio or FactoryTalk Live Data Test Client (p. 128).
See also: PanelView Plus 7 shows no data from the PLC and FactoryTalk View SE client cannot connect.
7. FactoryTalk Linx diagnostic tools
Chapter 10 (LNXENT-GR001Z p. 127) first asks you to check the system requirements and that FactoryTalk Administration Console is installed, then names two diagnostic tools; p. 30 adds FactoryTalk Live Data Test Client:
- FactoryTalk Diagnostics event log: review the events leading up to a problem (p. 127). The viewer is under "Start > All Programs > Rockwell Software > FactoryTalk Tools > Diagnostics Viewer" (LINX-GR001Z p. 30).
- Predefined items: for example, @ConnectionsActive shows how many CIP connections a path uses (pp. 127, 133).
- FactoryTalk Live Data Test Client: test reads and writes from FactoryTalk Linx, FactoryTalk View SE or RSLinx Classic (LNXENT-GR001Z p. 30).
CIP connections matter for going online. The guide's example: RSLinx Enterprise CPR 9 SR 1 and earlier opened up to five CIP connections (four read, one write) per Logix controller, so a controller or bridge module could run out; adding an HMI terminal could then disturb all terminals, or programming software might not go online. From FactoryTalk Linx 6.00 (CPR 9 SR 2), read connections are limited for devices with few connections (p. 132). FactoryTalk Diagnostics logs I_CLXDP_STARTED_ON_ROUTE when a CLX data provider starts, and I_CLXDP_MAX_READ_CONNECTIONS with the maximum number of read connections it will try to open (p. 133).
Do not enable FactoryTalk Linx unsolicited messages on a computer where RSLinx Classic or KepServerEx needs TCP/IP port 44818 (p. 134). For firewall ports, see FactoryTalk and Logix firewall ports.
Before calling for support
Have ready (LINX-GR001Z p. 41): serial numbers and version ("Help > About RSLinx Classic"), Windows version and service packs, hardware, the exact error text, what you were doing and what you have tried. Engineer needed on site: request support.
Frequently asked questions
Why does RSLinx Classic not show the PLC in RSWho?
Check that the driver is in "Configured Drivers" and that "Autobrowse" is selected; otherwise "Refresh" runs only one discovery cycle (LINX-GR001Z p. 24). If Studio 5000 cannot see the PLC but RSLinx Classic can, check which communication software Studio 5000 uses.
What does a red X on a device in RSWho mean?
RSWho recognised the device before but cannot reach it now, for example because it was unplugged (LINX-GR001Z p. 24). The FactoryTalk Linx Network Browser uses a red X the same way (LNXENT-GR001Z p. 49).
Why can FactoryTalk Linx not discover devices on another subnet?
Switches can block UDP broadcasts sent to another subnet, so Remote Broadcast finds nothing. Use Device List/Range with real IP addresses instead, up to 255 items (LNXENT-GR001Z pp. 48, 70).
Why does the RSLinx Classic title bar say Lite?
Without valid activation files, or after the seven-day grace period, RSLinx Classic runs as Lite, which has no OPC or DDE (LINX-GR001Z pp. 9, 43).
Sources
- Rockwell Automation, LINX-GR001Z-EN-E, RSLinx Classic Getting Results Guide, version 4.40.00, 11/2023 — pp. 9–14, 18, 22, 24, 30, 38, 41, 43, 55, 59–60
- Rockwell Automation, LNXENT-GR001Z-EN-E, FactoryTalk Linx Getting Results Guide, version 6.50.00, 09/2024 — pp. 25–26, 30, 41, 45, 48–49, 51, 53, 56, 69–70, 72–73, 76–80, 84–86, 100, 127–128, 132–134
Read 6 November 2026. This article paraphrases the sources and does not quote them; read the original documents before designing or working on a system.