Connecting to a CompactLogix

[mainstreetmark]

Howdy folks

I'm back out in the field on a job i did maybe 3 years ago. It has a 1769-L23E-QBFC1B, and all i really need to do is connect with it, and make a small change.

The offline project I have has no IP set. Further, the PLC never shows up in RSLinx. The IP I have for it (from years ago) is not pingable. I even tried a serial cable (with various null-modem adapters, and RSLinx autocnfigures).

So, what's happened here? It's forgotten it's IP? If it hasn't how can I learn what it is?

Should I try a DHCP server and see if it's asking for an IP?

 

[MartB]

You could try opening BootP and see if it displays it's IP address?

 

[mainstreetmark]

Yeah, I did that. I can ping it. I can see the device's webpage at the IP.

RSLinx thinks it's a "Unrecognized Device", and gives me the ol '?' on it.

 

[Mickey]

EDS file?

http://www.ab.com/networks/eds/cgi-bin/search.cgi

 

[mainstreetmark]

Yeah, I got them in there. I installed all CompactLogix EDS files, as well as one for "1769-L23E-QBFC1 Ethernet Port", which the webpage I can get to says it is.

No Go. RSLinx still says "Unrecognized Device". It does have an X through it, as well, indicating it can't .. what.. even talk to the thing? I can Ping it, and I can get to it's webpage.

Maybe I'll try plugging directly in, bypassing the ethernet switch?

 

[mainstreetmark]

Some new hints:

The webpage supplied by the 1769-L23E-QBFC1 says:

IP Address: 0.0.0.0
Status: Unconnected

..and the ethernet port has a red light on it, indicating some bad news.

But, how can i get to it's webpage, without a IP address assigned.

 

[Ken Roach]

Um... hmm. You shouldn't be able to get to the webpage if it has an unassigned IP address. I wonder if your browser is showing you a cached copy, or if the controller is mis-reporting 0.0.0.0 for some other reason.

Which LED, exactly, is red ?

The red X indicates that RSLinx Classic is getting a timeout connecting to the controller.

Is there a chance you have another controller on the same network, at the same IP address ? When you PING, then do an "ARP -A" and check the MACID that correlates to the IP address against the actual MAC ID printed on the controller sticker.

 

[mainstreetmark]

It's the red "NS" light on the ethernet port: "The port has detected that the assigned IP
address is already in use".

"arp -a" didn't return the mac address in question at all. very curious.

Is there a way to restart the bootp/dhcp process, short of rebooting the PLC and getting myself in big trouble?

----
edit: there's a blinking "MS" light, too, but the manual says that's normal. "The port firmware is being updated - Normal operation - no action is required." That leads me to believe the ETHERNET port is the one being updated. Why is it still flashing, after 3 hours?

 

[Ken Roach]

I would plug in the PC directly to the controller, or put them both onto a switch with nothing else on it.

"Duplicate IP" is pretty unambiguous. 99% of the time it means you genuinely have another device on the network with the same IP address.

The other 1% of the time there's a Hirschmann managed switch with a funky IP detection mechanism that causes false Duplicate IP errors.

 

[mainstreetmark]

You don't think this "updating firmware" light is suspect? Even with nothing plugged in, the "NS" light on the ethernet port remains on.

 

[Ken Roach]

Wait, with NOTHING in the RJ45 jack, the NS LED remains solid red ?

That sounds like a damaged port to me. The NS LED should be off if there's nothing plugged into it.

I seem to recall that a blinking Module Status LED is typical if there's no traffic addressed to the controller. That "updating firmware" state isn't the only reason for the MS LED to blink green.

In the past three years, is it possible that this flowchart was applied to the control system ?

 

[mainstreetmark]

Ok, I managed to reassign the IP of my computer to a new IP, and do a bunch of other windows network hackery, and plugged the ethernet cable directly into the PLC -- and noticed that the BOOTP server was asking for a new IP. It was still at 160.100.1.40, but at least i could re-assign it.

I pinged for 160.100.1.30, and noting it was empty, assigned that IP. Once i did, I ping'd it, and the PLC'd webpage now lists the current IP address (whereas before, it was 0.0.0.0), so that's a step forward! However, it still says "Unconnected".

And, yes, with no cable whatsoever plugged in, the "NS" light on the ethernet port remains "red", and the "MS" light is flashing.

I think the only thing i can do now is reboot the plc, huh?

 

[Ken Roach]

Rebooting would be a good step, yes. It's possible that once a duplicate IP is detected that the NS LED stays red until the controller is reset.

Can you browse the controller with RSLinx/RSWho over Ethernet yet ?

 

[mainstreetmark]

Fixed it.

I wound up deleting every setting and rebooting the PLC, and starting over with a fresh IP address. THe only thing that really ended up being different is the Gateway wasn't set properly in Tools->network settings. I don't really have a gateway on this network, it's only 2 devices, so I just set it to itself. Maybe that was the issue.

 

[Ken Roach]

Aha !

The BOOTP/DHCP Server Utility will not allow you to enter an IP address for a device that is not on the same subnet as the Default Gateway value in the Network Settings.

I've never tried to set the Gateway to the same IP address as one of my devices... it just never occurred to me. That definitely won't work.

If you aren't connecting the system to an outside network, just put 0.0.0.0 into the Default Gateway field.

On the 1756-ENBT I just tested, setting the Default Gateway equal to the IP Address didn't cause a red Network Status LED, but the CompactLogix might be different.