Jeremylacsd

OTL with no OTU

7 posts in this topic

Looking through the ladder logic on my program and came across an OTL instruction, and when I cross reference it, there's no OTU. Is this normal? It was my understanding any OTL instruction must have an OTU associated with it.

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There is no rule that states that in OTL instruction must have an OTU instruction. There are several cases that you might do this.

The programmer may of had some glitch that he was trying to catch and so he put that in there so that he could come back later and see it.

Probably the more common is that there is an HMI or other network device that is setting that bit to zero.

Also don't forget to look for manipulation at the word level such as a move instruction to B3:0 affecting B3:0/5.

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Thank you for the help, it was the HMI.

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^^ most likely answer

but

I think, but haven't verified, that an OTE turned off will unlatch an output too but I can't think of a good way to use it off the top of my head

 

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Just now, Jeremylacsd said:

Thank you for the help, it was the HMI.

Lol... posted as I was typing. 

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another common scenario is latching individual bits using OTL (for example alarms) and clearing them with FLL, CLR or MOV.

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On 2017-4-29 at 5:12 PM, Michael Lloyd said:

^^ most likely answer

but

I think, but haven't verified, that an OTE turned off will unlatch an output too but I can't think of a good way to use it off the top of my head

 

That would produce a "Duplicate  Destructive warning "  so frowned upon.

 

 

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