1794 AENT Comm Loss

SGreep

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Join Date
Nov 2012
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I am trying to figure out a way to detect a communication fault to a 1794 AENT remote module from a 1756-L55 Processor. I do not want to create a major fault on the controller, but i want some type of a safety to detect this fault and disable all assosiated outputs. Is there any status bits from the module that i could use to create a watchdog of some type?
 
You could use a Get System Value (GSV) instruction.

If you place the instruction onto a rung and press F1 to bring up the help, you will find what you are looking for.

Alternatively do a search on here.

Mark
 
Use a GSV.
Instance Name = The Name/tag of the AENT
Attibute Name = EntryStatus
Dest = Tag (int)

Then check to see if the Destination tag equals 16384 (4000 hex). If it is Communication to the device is okay. If not there is a comm fault and then your program can take action from there.

This can be used for any device setup in RSlogix under Ethernet including drives, HMIs, & 1756-ENxT

I typically do this on all Network Devices. If there are a lot I set up a sequencer to check only one or two each scan. I sometimes also set it up to only check if LedStatus of the main processor Not = 3 (GSV, Class name = MODULE, Attribute Name = LedStatus)
 
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Both Mark and bimini3's recommendations are part of the universal method of checking a Module Object's status.

The 1756-PM015 Programming Manual title is "Logix 5000 Controllers Information and Status".

It's the most complete reference to have on hand when you're doing this kind of detail programming in ControlLogix.

A quick and dirty method for detecting the connection status of a FLEX or POINT adapter that has a Rack Optimized connection (which is typical):

When you have a 1794 adapter on ControlNet or EtherNet/IP, there is a tag automatically generated for it that gives you 1 bit per slot for the status of any modules that are part of the Rack Optimized connection.

AdapterName:I.SlotStatusBits 0000_0000_0000_0000_0000_0000_0000_0000

If the connection to the adapter is lost entirely, all of those bits go true, which makes the value of the whole DINT type tag = -1.
 
If you're worried about output module behavior in the event of communication loss, you can configure your Flex I/O output cards to behave a certain way when communication is lost. I know this is also the case with 1734 Point I/O, it's my guess that it's this way on all AB output modules.

Module_Communication_Loss.png
 
Hello
I was wanting to know also how to read the status bit from the 1794-AENT Flex?
I have a 1769-L32E compact logix controller with 1794-AENT FLex communicating back to the 1769-L32 compact logix controller

if i lose communications to the 1794-AENT I want to be able to know this
Which bit do I use to see the communication status of the 1794-AENT?


thanks for helping
 
Hello
I was wanting to know also how to read the status bit from the 1794-AENT Flex?
I have a 1769-L32E compact logix controller with 1794-AENT FLex communicating back to the 1769-L32 compact logix controller

if i lose communications to the 1794-AENT I want to be able to know this
Which bit do I use to see the communication status of the 1794-AENT?


thanks for helping

Read the above solutions. There is no status bit...use the GSV entrystatus and compare it as outlined above.
 
Read the above solutions. There is no status bit...use the GSV entrystatus and compare it as outlined above.

To add to the status bit, some devices have a "status bit" but when you lose comms the status bit doesn't update until comms are regained.
 
It seems that the GSV statement to monitor the network connection between the two devices is what I need to do, but I havent done this before and the help files aren't too great.

it would be nice to get a good explanation from someone that has experience with using this statement

GSV_Rung.jpg


I'm not sure how to configure the settings
-Class Name (Is this the name of the Flex 1794-AENT module I'm wanting to monitor?)
-Instance Name
-Attribute Name
-Dest

I appreciate the help
 
Class Name = Module
Instance Name is the device....just drag your device name from the I/O tree
Attribute Name = EntryStatus
Dest = a DINT tag that you declare

Once you program this instruction, DIV EntryStatus by 4096 into another DINT tag that you declare, and compare this second DINT tag to a value of 4. If it's equal to 4, then your comms are OK. Anything else, your comms are not ok.

The only other suggestion is you might want to condition your GSV call on some interval, such as every second or every few seconds...whatever you can live with for detecting a fault. Because each GSV call takes some system overhead to accomplish, so if you're calling it every scan when you don't need to, its not efficient to do so. Probably won't matter if that's your only GSV and only ethernet device. But if you're polling 100 devices, then it adds up.
 
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