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MicroLogix 1500 Instructions

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I am wondering if there is a way using RSLogix 500 with a MicroLogix 1500 LPR processor to figure out cube root. It is not an available instruction. Thanks

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XPY was greyed out when I tried to use it in a 1500 LRP... Bummer. X raised to the power of 1/3 is apparently not available in the mini-me of AB processors...

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This might work LINK The link opens a PDF file with the equation for cube root in it. It's iterative Edited by Michael Lloyd

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Attached is one way of doing the cube root by repeatedly calling a subroutine until the result is good. It was done on for an 1100 since the free software doesn't support the 1500. The formula is This Answer = ((2 * Previous Answer) + (Target / PreviousAnswerSquared))/3 Larger 'Targets' take more passes to arrive at the answer. If you have a certain range of 'Targets' you may want to start at a different initial 'Answer' than '1'. Cuberoot.zip Edited by b_carlton

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Thanks this looks like it will do the trick.

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I plugged the formula into Excel and expanded down to see how many itirations it took for different starting points and the effect of different starting guesses.

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