S7-200 Minor Fault - 'Input interrupt to a point already assigned to an HSC'

antsrealm · Mar 20, 2016

Hi,

We have a dosing system that uses the 224XP REL 02.01 CPU. It has a encoder input wired to input I0.1 and monitors the position and speed of the machine in order to trigger the dosing.

We have had some problems with it and I suspect there is an issue in the code as the few inputs it has seem ok.

The encoder has been replaced just in case and is ok.

Not sure why but the PLC info shows a minor fault with the following description....

'Input interrupt to a point already assigned to an HSC'

It points to INTERRUPTS program at network 4

I don't know enough about siemens to understand why this has occurred. Can someone help me to understand this?

Thanks,

gclshortt · Mar 20, 2016

http://www.kjit.bme.hu/images/stories/targyak/plctechnika/s7-200_e.pdf

DTCH disassociates an interrupt event EVNT from all interrupt routines and disables the interrupt event.
In your case event 2 is the I0.1 Rising edge.

ATCH associates an interrupt event EVNT with an interrupt routine number INT and enables the interrupt event.
In your case event 11 is the Timed interrupt 1 SMB35
This may be already assigned in your logic in a place above these rungs.

Hope this helps,

BryanG · Mar 20, 2016

You have two things using I0.1. The encoder and HSC are using it, and in the block of code you posted you are Detaching Event 2 which is a Rising Edge Interrupt on I0.1.

antsrealm · Mar 21, 2016

Thanks for the replies and the PDF.

I'm trying to get my head around the interrupts. How do they work? and what is the relation with the event number?

I have a basic idea but feel like it's not clear.

BryanG · Mar 21, 2016

Don't want to look like a 'Smarty Pants', but they Interrupt the main program to do something else by running a separate INT Program Block, and then return back to the main program afterwards. The main program runs cyclically, an Interrupt can Interrupt the cycle at any point to run the separate INT Program Block, plus nested SBR subroutines.
Here is the S7-200 range interrupt table.

antsrealm · Mar 22, 2016

Thanks, I think I'm across these interrupts now.

In regards to the minor fault and ENO =0 that suggests to me that an output is not enabled as a result of this fault. Does that mean an interrupt is not running or not associating as it should be. As that may explain why part of our process is not working?

BryanG · Mar 22, 2016

I don't know which ENO you are looking at for you decide that there is a problem. You could add a few M bits and watch their values in a Watch Table, so that you know if a function is failing. The minor fault may be enough to cause the program to malfunction, you would have to try changing it so that you don't share I0.1 between two functions. If you have the spare inputs you can easily used a different one for the Rising Edge detection, you will have to modify the associated ATCH and DTCH to use the different Interrupt input.

antsrealm · Mar 22, 2016

Bryan,

Thanks for the reply. Yeah I saw that in the manual. Since I have a minor fault with error 2 and error 2 indicated ENO = 0 I assume that means the output enable of the attach instruction isn't executing and therefore that event does not run that program.

antsrealm · Mar 22, 2016

There is also only 1 ATCH instruction for event 11 in the whole program ??

antsrealm · Mar 22, 2016

The point it's assigned to "ENCODER_SPEED" is only assigned to that one ATCH isntruction as well so I don't see where the conflict is coming from.

antsrealm · Mar 22, 2016

After checking all the ATCH instruction there is two that use event 12 and two that use event 32. After reading the manual it states...

"but one event cannot be concurrently attached to multiple interrupt routines"

I'm not sure if they are detached before attaching the other one but that hasn't been a problem in the past and neither is in the network indicated by the minor fault.

So i'm struggling to understand what is wrong with network 4 in the INTERRUPTS routine??

BryanG · Mar 22, 2016

So i'm struggling to understand what is wrong with network 4 in the INTERRUPTS routine??

I am guessing that it is complaining about Network 4 because that is the first place that the Interrupt for Event 2 is programmed. If you deleted the Detach Instruction the error would probably move to the point where you have the Event 2 Attach instruction.

But the big thing is:
You have the HSC that is using I0.1 and you have a Rising Edge Interrupt that is using I0.1.
I0.1 can't be used for both functions. So use another input for the Rising Edge and modify the program to suit.

antsrealm · Mar 22, 2016

Ok perfect.

Now on the topic of that last bit in bold. On input I0.1 we have an encoder wired up. So what is the difference between the HSC and the rising edge. Obviously it needs to be used for the encoder but isn't the rising edge event also triggered on the rising edge of the encoder input. Or should I just parallel the same encoder signal to two different inputs and use one as the HSC and one as the rising edge event?

Weird thing is that this system was working a week ago.

BryanG · Mar 22, 2016

So what is the difference between the HSC and the rising edge.

The HSC counts incoming pulses, the Rising Edge Interrupt looks for a rising edge, so they might be reading the same signal but have very different functions.

Or should I just parallel the same encoder signal to two different inputs and use one as the HSC and one as the rising edge event?

Doing this should get rid of the non-fatal error message, but if this was working last week the error message may have been there all the time and not caused an issue. The non-fatal error may be a complete 'red herring' and after fixing it you will be back to finding the problem.

antsrealm · Mar 22, 2016

Yeah you might be right, could well be a red herring. At least I now understand the interrupts and should be able to chase the fault a little better.

Thanks for the help.

S7-200 Minor Fault - 'Input interrupt to a point already assigned to an HSC'

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