RSlinx won't see a PLC on the network

I am running RSlinx Classic.

I have 4 Micrologix 1500 PLC's (with Net-ENI's), one old Panelview, and one Panelview Plus. All on AB_ETH-1 driver.

The issue is I lost RSlinx communication with one Micrologix PLC (192.168.8.3). The PLC has a associated PanelViewPlus (192.168.8.8) The Panelview Plus and the PLC are communicating, but I can't see the PLC now.

Note: I could see the PLC yesterday, I couldn't see it this morning, it came on network randomly (I don't know what I did but it showed up and I was able to go online with the PLC) then it dropped out again and I can't see it.

I am not allowed to re-boot the PLC, (because they don't want me to shut the equipment down ) which would be my go-to, first step.

Last piece to the issue, they want to take the PLC data over to BACnet, so there is a RTA device (Real Time Automation). I can't get it to communicate with PLC.3. I have it removed from the network until I resolve whatever is going on with RSlinx, BUT, I had RSlinx communications (temporarily) , I put the RTA Device on line, it seemed to communicate. I lost RSlinx communication, but seemed to maintain RTA Gateway coms. I unplugged Gateway thinking it 'communications was possibly related to my RSlinx issue. removing RTA Gateway had no effect, so I tried to bring it back on line and it doesn't see the PLC either.

I am thinking it may all be related to the NET-ENI, but I don't know.

I am at a loss. I can ping the PLC, The screen communicates with the PLC , but RSlinx is showing the PLC as a red X.

Any thoughts?

You are very likely running into the 1761-NET-ENI's notoriously small TCP connection capacity.

The Net-ENI supports six simultaneous TCP connections; two outgoing, two incoming, and two in either direction.

It's not hard for an active network to accidentally use up some of the available TCP connections with things like RSLinx Classic and RSLinx Enterprise browsing sessions.

The best diagnostic tool, if you're up for it, is to use Telnet to connect to the Net-ENI and interrogate its onboard diagnostics. This is described in RA Knowledgebase Article ID #27418 (Access Level: TechConnect). A more concise explanation of using Telnet to do a remote reset of the Net-ENI is in Knowlegebase Article ID #68548 (Access Level: Everyone).


If your system can tolerate a temporary loss of communication, you can reboot just the Net-ENI via Telnet or by disconnecting its power and/or unplugging it from the MicroLogix controller. The MicroLogix 1500 has a serial port with 24V auxiliary power to run the Net-ENI/DNI/AIC devices, so sometimes they are powered off the controller port. There is an "external/internal" power selector switch on the Net-ENI.

Thanks Ken,

I did do a re-boot on the PLC when I thought no one would notice and it fixed all my RSlinx problem and my RTA Gateway (BACnet Interface) issue.

If I would have just done it first, like I knew I should, I would have saved several hours.

Now I will study up on the tech article you linked.

Thanks