HCS12 datasheet(349/452 Pages) FREESCALE

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S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

349

9.4.2 Abnormal Membership Function Definitions

In the CPU12, it is possible (and proper) to define “crisp” membership

functions. A crisp membership function has one or both sides vertical

(infinite slope). Since the slope value $00 is not used otherwise, it is

assigned to mean infinite slope to the MEM instruction in the CPU12.

Although a good fuzzy development tool will not allow the user to specify an

improper membership function, it is possible to have program errors or

memory errors which result in erroneous abnormal membership functions.

Although these abnormal shapes do not correspond to any working

systems, understanding how the CPU12 treats these cases can be helpful

for debugging.

A close examination of the MEM instruction algorithm will show how such

membership functions are evaluated. Figure 9-5 is a complete flow diagram

for the execution of a MEM instruction. Each rectangular box represents one

CPU bus cycle. The number in the upper left corner corresponds to the cycle

number and the letter corresponds to the cycle type (refer to Section 6.

Instruction Glossary for details). The upper portion of the box includes

information about bus activity during this cycle (if any). The lower portion of

the box, which is separated by a dashed line, includes information about

internal CPU processes. It is common for several internal functions to take

place during a single CPU cycle (for example, in cycle 2, two 8-bit

subtractions take place and a flag is set based on the results).

Consider 4a: If (((Slope_2 = 0) or (Grade_2 > $FF)) and (flag_d12n = 0)).

The flag_d12n is zero as long as the input value (in accumulator A) is within

the trapezoid. Everywhere outside the trapezoid, one or the other delta term

will be negative, and the flag will equal one. Slope_2 equals zero indicates

the right side of the trapezoid has infinite slope, so the resulting grade

should be $FF everywhere in the trapezoid, including at point_2, as far as

this side is concerned. The term grade_2 greater than $FF means the value

is far enough into the trapezoid that the right sloping side of the trapezoid

has crossed above the $FF cutoff level and the resulting grade should be

$FF as far as the right sloping side is concerned. 4a decides if the value is

left of the right sloping side (Grade = $FF), or on the sloping portion of the

right side of the trapezoid (Grade = Grade_2). 4b could still override this

tentative value in grade.

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