Page 236 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

7,6 Fuzzy Logic 21.3

If quiz 1 is A, quiz 2 is A, homework assignment is A, then course is A.+,

Rules can be weighted. The confidence value for a rule is determined as usual by
finding the smallest rule antecedent. Before applying this value to the consequents for the
rule, the value is multiplied by a fraction from zero (rule disabled) to $FF (rule fully
enabled). The resulting modified confidence value is then applied to the fuzzy outputs,
Equation (19) illustrates that the output for a set of rules is the output Sj for each rule
times a weight Fj, divided by the sum of the weights.
The rules can reflect nonlinear, but deterministic, relationships. For instance, if a
student gets a B on the first quiz and an A on the second quiz, the instructor may decide
that the course grade is A-, but if a student gets an A on the first quiz and a B on the
second quiz, the instructor may decide that the course grade is B+. But if the student also
did poorly in lab work, then the course grade might be B-, to give the student some
incentive to get to work. That is, if quiz 1 is A, quiz 2 is B, and lab is not C, then
course is B+, but if quiz 1 is A, quiz 2 is B, and lab is C, then course is B-. In the
limit, if there are n input variables and each input variable is associated with m linguistic
*
* Fuzzification step:
*
FUZZIFY: LDX #INPUT_MFS ;Point at member function definitions
LDY #FUZ_INS ;Point at fuzzy input vector
LDAA CURRENT__INS ;Get first input value
LDAB #7 ;7 fuzzy values per input
GRADJLOOP: MEM ;Evaluate a member function
DBNE B,GRAD_LOOP ;For 7 labels of 1 input
LDAA CURRENT_INS+1 ;Get second input value
LDAB #7 ;7 fuzzy values per input
GRAD_LOOP 1: MEM ;Evaluate a member function
DBNE B,GRAD_LOOP1 ;For 7 fuzzy values of 1 input
* Rule Evaluation step:
LDAB #7 ;Loop count
RULE_EVAL: CLR 1,Y+ ;Clr a fuzzy out & inc ptr
DBNE B,RULE_EVAL ;Loop to clr all fuzzy Outs
LDX #RULE_START ;Point at first rule element
LDY #FUZ_INS ;Point at fuzzy ins and outs
LDAA #$FF ;Init A (and clears V-bit)
REV ;Process rule list
* Defuzzification step:
DEFUZ s LDY #FUZ_OUT ;Point at fuzzy outputs
LDX #SGLTN_POS ;Point at singleton positions
LDAB #7 ;7 fuzzy outs per COG output
WAV ;Calculate sums for weighted av
EDIV ;Final divide for weighted av
TFR Y,D ;Move result to accumulator D
STAB COG_OUT ;Store system output

Figure 7.23. A Fuzzy Inference Kernel