sngX1 := UINT_TO_REAL (uintX1);
sngX2 := UINT_TO_REAL (uintX2);
sngY1 := UINT_TO_REAL (uintY1);
sngY2 := UINT_TO_REAL (uintY2);
sngX := UINT_TO_REAL (uintX)*EXPT (10.0, uintDecPtDiff);

IF sngX <= sngX1 THEN
    uintY := REAL_TO_UINT (sngY1);
ELSIF sngX >= sngX2 THEN
    uintY := REAL_TO_UINT (sngY2);
ELSE
    uintY := REAL_TO_UINT (sngY1+(sngY2-sngY1)/(sngX2-sngX1)*(sngX-sngX1));
END_IF;

我没用过欧姆龙的，不过这个看起来也不难理解吧。
sngX1 := UINT_TO_REAL (uintX1);这个是数据类型转换，整型转换成浮点型，
IF sngX <= sngX1 THEN
    uintY := REAL_TO_UINT (sngY1);
ELSIF sngX >= sngX2 THEN
    uintY := REAL_TO_UINT (sngY2);
比较，转换，赋值。
ELSE
    uintY := REAL_TO_UINT (sngY1+(sngY2-sngY1)/(sngX2-sngX1)*(sngX-sngX1));
END_IF;
计算，赋值。