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S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

5.15.3 Fuzzy Logic Weighted Average Instruction

The weighted average (WAV) instruction computes a sum-of-products and

a sum-of-weights used for defuzzification. To be usable, the fuzzy outputs

produced by rule evaluation must be defuzzified to produce a single output

value which represents the combined effect of all of the fuzzy outputs. Fuzzy

outputs correspond to the labels of a system output and each is defined by

a membership function in the knowledge base. The CPU12 typically uses

singletons for output membership functions rather than the trapezoidal

shapes used for inputs. As with inputs, the x-axis represents the range of

possible values for a system output. Singleton membership functions

consist of the x-axis position for a label of the system output. Fuzzy outputs

correspond to the y-axis height of the corresponding output membership

function. The WAV instruction calculates the numerator and denominator

sums for a weighted average of the fuzzy outputs. Because WAV requires

a number of cycles to execute, it can be interrupted. The WAVR

pseudo-instruction causes execution to resume at the point where it was

interrupted.

Table 5-13. Fuzzy Logic Instructions

Mnemonic

Function

Operation

MEM

Membership

function

µ (grade) ⇒ M(Y)

(X)

+ 4 ⇒ X; (Y) + 1 ⇒ Y; A unchanged

if (A) < P1 or (A) > P2, then

µ = 0, else

µ = MIN [((A) – P1) × S1, (P2 – (A)) × S2, $FF]

where:

A = current crisp input value

X points to a 4-byte data structure

that describes a trapezoidal membership

function as base intercept

points and slopes (P1, P2, S1, S2)

Y points at fuzzy input (RAM location)

Continued on next page

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