Using FSC instruction in Controllogix

ettikudiappan

Member
Join Date
Apr 2002
Location
Singapore
Posts
131
I am having trouble using the FSC instruction in RsLOgix 5000. I want to search an array in a single scan and only on a rising edge. So I have an ONS instruction followed by a FSC instruction in "ALL" mode. The first time the rung-in condition goes from false to true, the array is searced alright. I reset the inhibit bit whether a match is found or not. But when the rung goes from false to true again, the FSC instruction is not executed. I have overcome this by reseting the found bit and also setting control.pos to zero. My question is, is it right way to use the instruction? From the help files I gather that I need to reset only the inhibit bit to start another search.
 
The FSC stops searching the array on the first true comparison and sets the IN and FD bits. Provided the rung remains true, resetting the IN bit will enable the search to continue from the current position to the next true comparison or the end of the array. Once the whole array has been searched, the DN bit is set.

Your use of the ONS is probably unnecessary since the FSC is initiated by transition. I assume you wish to search for the first true compare only and start all searches at the beginning of the array. To accomplish that, you should reset (RES) the control tag and unlatch (OTU) the IN bit before each initiation of the FSC. For completeness, unlatch the FD bit as well.
beerchug
 

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