What is Download mode?

I have an AllenBradley CompactLogix v20.12PLC that keeps going into
‘Connecting Download Mode’.
This will last for days and days and then correct itself.
While in ‘Connecting Download Mode’ the tags are not updating.
What is causing this and how do I correct it?
I have 3 other CompactLogix PLC on the same server/gateway and they operate issue free.

From what I can see the legacy CLX driver reads the processor mode as part of its periodic status request.

If it’s not RUN or PROGRAM then the connection state is considered invalid. One of things the mode can apparently indicate is a download is in progress, but I’m not sure where this is documented, or how these modes were determined.

Are the other 3 PLCs the same version?

Do you have any update on this issue?
Maybe it could help me too.

Just got a ticket here with the same problem, any hints?

I am experiencing this same issue- The PLC has been connected and running fine for a couple years and suddenly Ignition can't seem to connect to it anymore. The PLC is reachable over the network. Any ideas?

Has its firmware been changed?

No, neither the PLC firmware nor code have been changed in years.

Digging around in the source for the legacy driver, it seems this status is only returned if the comms are "inactive" for some reason, which should be accompanied by a log message in the gateway about the comm state changing.

This happens when the controller fails to respond, or responds with an error code, to the periodic status requests.

Thanks Kevin, I'll keep looking into it with that information. Once I figure it out, I'll post an update.

It seems it was something simple- I noticed that although I was able to ping the PLC from other computers on the network, I was unable to ping it from the Ignition server. Our IT apparently made a network change which prevented the Ignition server from communicating with that subnet. That particular subnet only had one Ignition-connected PLC on it. I'm not sure why it showed downloading mode, but after I disabled and re-enabled the connection on the OPCUA devices screen, it showed the usual cycling connecting...disconnected... status.