Why did my SLC5/05 procesor node # change?

Hi everyone, it's a cold and rainy/snowy day in Kentucky!

I ran into this problem and can't figure out why it happened, or what's the best way to fix.

System configuration:
- SLC5/05 and Micrologix PLCs
- Ethernet and serial port comms
- Ethernet dataradios for remote telemetry


I have been working on some pump station telemetry issues all day, using a single laptop with RSLogix 500 Starter to modify programs and download them to various PLCs at different sites.

Then I went to the main plant to download a final update to the MTU, I got a notice in RSLogix 500 that the Processor Node number was different between the loaded program and the PLC. It wanted me to confirm or cancel. I cancelled because I was sure the node number had previously been 48d, but now it was being reported as 0d.

Sure enough, looking in the Controller Properties of the project, it shows the Processor Node ID as 48d. So I opened a new RSLogix project and uploaded the entire running program from the PLC. In this copy, the Controller Properties shows the Processor Node ID as 0d.

Screenshot of the two projects side by side: http://is.am/y9sm
Left-hand project is an upload directly from the PLC. Right-hand side is the saved project that I was trying to download.

Here's a screenshot of the dropdown box in Controller Properties showing the Last Configured selections: http://is.am/y9sp

Also when browsing with Who Active, clicking on the processor it shows the node ID as 0d. Screenshot: http://is.am/y9sn

I had downloaded several changes to this PLC earlier in the day with no issues.

Why would the Node ID change? And how can I change the PLC's node ID back to the 48d value that it was before? Does it even matter? Should I just download the project anyway, or will it break something?

I checked the programs for all the other PLCs in the network, and none of them refer to Node 48d in their MSG commands. They all use IP communications except for one unit that communicates to the serial port of this MTU, and its target device is Node 1, and its comms are still working.

Thanks for any advice!

Sounds like it doesn't matter, since it is the master and neither 0 nor 48 is in use.

On a similar note, I have a ML1400 on my test bench that TWICE changed its subnet mask to 0.0.0.0 when I performed downloads. The offline file was 255.255.255.0. I fixed that with the LCD and onboard buttons. Later it started complaining about a duplicate IP address (and on this isolated network, that was not possible). I fought the duplicate IP address a little bit and couldn't solve it. Got done with my testing and dumped a different program in it for a different project and it is working fine now.

Anyhow, it probably did happen when you downloaded earlier. I have not looked to see if it is possible to programmatically change the node ID for the serial port, and don't have software handy at the moment.

OK thanks for the info. How would I go about changing the ID back to the old value? I can't find an option to change it in the RSLogix 500. Do I have to connect to the PLC via a serial port to achieve this?

Thanks!

The Controller Communications tab under Controller Properties is where you can change the node number.

I should have looked at your screen shots before I spouted off. I was on my slow home internet so I didn't even open them. The screenshots you posted show ethernet communications with a node number that is probably irrelevant. I am not 100% sure, but I think that node number you see there is related to where in the list in RSWho your PLC showed up the last time you set the Systems Comms settings for the project that is saved on your PC.

So, I don't even think that the node number you see makes any difference and isn't even present in the PLC. I don't even think it should be visible in that window when using Ethernet, but there is probably some legacy reason they make it visible.