HCS12 datasheet(346/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

346

Freescale Semiconductor

are automatically updated by four and one so they point at the next

membership function and fuzzy input respectively.

Line 7 loads the current value of the next system input. Pointers in X and Y

already point to the right places as a result of the automatic update function

of the MEM instruction in line 5.

Line 8 reloads a loop count.

Lines 9 and 10 form a loop to fuzzify the seven labels of the second system

input. When the program drops to line 11, the Y index register is pointing at

the next location after the last fuzzy input, which is the first fuzzy output in

this system.

Line 11 sets the loop count to clear seven fuzzy outputs.

Lines 12 and 13 form a loop to clear all fuzzy outputs before rule evaluation

starts.

Line 14 initializes the X index register to point at the first element in the rule

list for the REV instruction.

Line 15 initializes the Y index register to point at the fuzzy inputs and outputs

in the system. The rule list (for REV) consists of 8-bit offsets from this base

address to particular fuzzy inputs or fuzzy outputs. The special value $FE is

interpreted by REV as a marker between rule antecedents and

consequents.

Line 16 initializes the A accumulator to the highest 8-bit value in preparation

for finding the smallest fuzzy input referenced by a rule antecedent. The

LDAA #$FF instruction also clears the V-bit in the CPU12’s condition code

rule list processing, the V bit is toggled each time an $FE is detected in the

list. The V bit indicates whether REV is processing antecedents or

consequents.

Line 17 is the REV instruction, a self-contained loop to process successive

elements in the rule list until an $FF character is found. For a system of 17

rules with two antecedents and one consequent each, the REV instruction

takes 259 cycles, but it is interruptible so it does not cause a long interrupt

latency.

Lines 18 through 20 set up pointers and an iteration count for the WAV

instruction.

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