HCS12 datasheet(372/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

372

Freescale Semiconductor

The meaning (reflected in membership function shape and position) of the

labels “close” and “fast” will be different for a teenager than they are for a

grandmother, but both can accomplish the goal of stopping. It makes

intuitive sense that the exact shape of a membership function is much less

important than the fact that it has gradual boundaries.

9.7.2 Rule Evaluation Variations

The REV and REVW instructions expect fuzzy input and fuzzy output values

to be 8-bit values. In a custom fuzzy inference program, higher resolution

may be desirable (although this is not a common requirement). The CPU12

includes variations of minimum and maximum operations that work with the

fuzzy MIN-MAX inference algorithm. The problem with the fuzzy inference

algorithm is that the min and max operations need to store their results

differently, so the min and max instructions must work differently or more

than one variation of these instructions is needed.

The CPU12 has MIN and MAX instructions for 8- or 16-bit operands, where

one operand is in an accumulator and the other is a referenced memory

location. There are separate variations that replace the accumulator or the

memory location with the result. While processing rule antecedents in a

fuzzy inference program, a reference value must be compared to each of

the referenced fuzzy inputs, and the smallest input must end up in an

accumulator. The instruction

EMIND

2,X+

;process one rule antecedent

automates the central operations needed to process rule antecedents. The

E stands for extended, so this instruction compares 16-bit operands. The D

at the end of the mnemonic stands for the D accumulator, which is both the

first operand for the comparison and the destination of the result. The 2,X+

is an indexed addressing specification that says X points to the second

operand for the comparison and it will be post-incremented by 2 to point at

the next rule antecedent.

When processing rule consequents, the operand in the accumulator must

remain constant (in case there is more than one consequent in the rule), and

the result of the comparison must replace the referenced fuzzy output in

RAM. To do this, use the instruction

EMAXM

2,X+

;process one rule consequent

The M at the end of the mnemonic indicates that the result will replace the

referenced memory operand. Again, indexed addressing is used. These two

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