1756-CNB/E OK LED Flashing Green

[Saulo35]

Hi,

Short version: the OK LED of a 1756-CNB/E in a redundant system flashes green.

The alphanumeric display cycles OK / %C30 / KpIv / nC00 / A#02 (the number after the %C varies - it's the CPU loading - it's OK)

I have a redundant system as follows:

Chassis 1
1756-A4
0 - 1756-CN2/B/20.020.602800 - Node 5
1 - 1756-EN2T/C/5.008.700300 - IP Address 192.168.1.2
2 - 1756-L61/B/20.054.110
3 - 1756-RM/B/3.003.7

Chassis 2 (Identical to Chassis 1)
1756-A4
0 - 1756-CN2/B/20.020.602800 - Node 5
1 - 1756-EN2T/C/5.008.700300 - IP Address 192.168.1.2
2 - 1756-L61/B/20.054.110
3 - 1756-RM/B/3.003.7

I/O Chassis
1756-A13
0 - 1756-CNB/E/11.004 - Node 1
1 - 1756-CNB/E/11.004 - Node 2 (THIS IS THE ONE FLASHING)
2 - 1756-IF16/A/1.005
3 - 1756-IF16/A/1.005
4 - 1756-OF8/A/1.005
5 - 1756-OF8/A/1.005
6 - 1756-OF8/A/1.005
7 - 1756-OW16I/A/3.002
8 - 1756-OW16I/A/3.002
9 - 1756-OW16I/A/3.002
10 - 1756-IA16/A/3.003
11 - 1756-IA16/A/3.003

and a PanelView Plus 1500 at IP Address 192.168.1.1

Everything is working well, the redundant modules are doing their job (one is PRIM and the other is SYNC, the IP Addresses and ControlNet nodes flip when power to PRIM goes off, etc.).

The only consequence I see is that when I disconnect the ControlNet cable from the CNB in slot 0, all the I/O modules' OK LEDs turn red and the PRIM processor's IO LED starts blinking. Looks like the CNB in Slot 1 is not "takingg over". If I disconnect from the CNB in slot 1, nothing happens to the I/O modules.

I could not find an explanation for CNB's OK LED flashing green other than accompanied by error messages "CNFG ERR" and "NET ERR", which I don't have.

Any clues will be appreciated.

Thank you

 

[iant]

sorry I dont know - I just want to track this thread.
I dont think both CPU's can have the same IP address

 

[Saulo35]

Hi iant,

Both Ethernet cards have the same IP address and both ControlNet cards have the same node address because the redundant modules take care of flipping them around when needed. That way, the rest of the world (say, the HMI) notices no change (they point always at the same IP address or ControlNet node).

You just have to reserve the next address up (192.168.1.3 and Node 6 in this case) because those are the addresses used by the Secondary (SYNC) Ethernet card and ControlNet adapter.

Take care

 

[Contr_Conn]

Did you put node 2 in i/o config?
Probably not.
Then nothing is wrong, it just tells no connection.
If you have it in the tree then post sceenshot of the general and connection tab.

 

[Contr_Conn]

Just to clarify:
Node2 is not designed to be active in your system, this is not redudnand backup for node 1
Redudndancy system must have two i/o nodes to switchover correctly. So system designer added node 2 to be a place holder.
Again nothing is wrong

 

[Saulo35]

Thank you, Contr_Conn.

Yes, Node 2 is in the I/O Configuration. I am attaching the General and Connection tabs of both ControlNet cards. I see that the ControlNet card in Slot 0 (node 1) has a Parent while the other does not.

Thanks for Node 2's role clarification.

Cheers,

 

[Contr_Conn]

Node 2 properties posted are as lited on the "backplane", not from Controlnet connection.

Can you post shot of expanded "controlnet" tree below node 5 ?
I would guess you probably will see "01" and "05" only

Again, nothing wrong with your system, node 2 is just a dummy network holder, it must be present.

 

[Saulo35]

You are right, the tree shows just Nodes 1 and 5. Please see attachment.

Regarding "Node 2 properties posted are as lited on the "backplane", not from Controlnet connection.", is there anything I should do about that?

Thank you,

 

[Contr_Conn]

All looks ok to me, it does not matter if node 2 is listed on backplane or not, it does not do anything

just don't expect it to take over if node 1 connection lost.

 

[Saulo35]

OK. Thank you for all your help.

 

[MichaelG]

I thought that to have redundant control net that you required to use the CN2R (redundant media) and that only one CNet card per IO rack was needed

 

[Contr_Conn]

I thought that to have redundant control net that you required to use the CN2R (redundant media) and that only one CNet card per IO rack was needed

This is correct statement, but in this example second card does not add any redundancy, it actualy does almost nothing, it just sitting on the wire.
Second I/O node (node 2 in this case) must be present during switchover to keep network valid.
Read the redundancy manual, it clearly explains why you need a second node.

 

[MichaelG]

This is correct statement, but in this example second card does not add any redundancy, it actualy does almost nothing, it just sitting on the wire.
Second I/O node (node 2 in this case) must be present during switchover to keep network valid.
Read the redundancy manual, it clearly explains why you need a second node.

ahh the light dawns - all the systems that I have worked on had multiple IO nodes so that limitation never came up
thanks