Arithmetic instructions
470
Part III FP Instructions
Limitations of the output value y:
If the input value x is smaller than the x-coordinate of the first reference point (P1: x < x1), the
output y is set to the first reference point’s y-coordinate (output y = y1, horizontal dashed line in the
graph’s upper left corner).
If the input value x is greater than the x-coordinate of the last reference point (P8: x > x8), the
output y is set to the last reference point’s y-coordinate (output y = y8, horizontal dashed line in the
graphic’s upper right corner).
DUT for the xy value pairs (reference points P1, P2, ...):
The reference points (P1, P2, ...) are copied to the function via an DUT-type variable that contains
the number of reference points and the xy value pairs (number; x1, x2, ...; y1, y2; ...).
Structure of the DUT:
1. Entry: Variable of the data type INT that contains the number of reference
points.The number of reference points (xy value pairs) can be set anywhere between 2 ... 100. In the
graph, eight reference points (P1 ... P8) are used.
2. Entry: Variable of the data type ARRAY [0..z] OF INT that contains the x values.
Here z represents the place marker for the number of reference points (see entry 1).
3. Entry: Variable of the data type ARRAY [0..z] OF INT that contains the y values.
Here z represents the place marker for the number of reference points (see entry 1).
Important information:
x values
The x values have to be entered in ascending order (x1 < x2 < x3 < ...). If the x values are the
same (e.g. x2 = x3 = x4) the reference points P2(x2,y2) and P3(x3,y3) are ignored.
Overflow of the function:
In order to avoid an overflow in the calculation, neighboring reference points must fulfill the
following conditions:
|ya - yb| < 32767
|x - xb| < 32767
|(ya - yb)*(x - xb)| < 32767
|xa - xb| < 32767
Accuracy of the calculation:
This function can only process whole numbers. Numbers that follow the decimal point are cut out
when calculating the value y. For example, if at the position x, y = 511,13, the function returns the
value 511.
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