HCS12 datasheet(371/452 Pages) FREESCALE

371 / 452 page

S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

371

Figure 9-13. Endpoint Table Handling

The basic idea is to find the segment of interest, temporarily build a

1-segment table of the correct format on the stack, then use TBL with stack

relative indexed addressing to interpolate. The most difficult part of the

routine is calculating the proportional distance from the beginning of the

segment to the lookup point versus the width of the segment

((XL–XB)/(XE–XB)). With this type of table, this calculation must be done at

run time. In the previous type of table, this proportional term is an inherent

part (the lowest order bits) of the data input to the table.

Some fuzzy theorists have suggested membership functions should be

shaped like normal distribution curves or other mathematical functions. This

may be correct, but the processing requirements to solve for an intercept on

such a function would be unacceptable for most microcontroller-based fuzzy

systems. Such a function could be encoded into a table of one of the

previously described types.

For many common systems, the thing that is most important about

membership function shape is that there is a gradual transition from

non-membership to membership as the system input value approaches the

central range of the membership function.

Examine the human problem of stopping a car at an intersection. Rules such

as “If intersection is close and speed is fast, apply brakes” might be used.

BEGIN

LDY

#TABLE_START-2

;setup initial table pointer

FIND_LOOP

CMPA

2,+Y

;find first Xn > XL

;(auto pre-inc Y by 2)

BLS

FIND_LOOP

;loop if XL .le. Xn

* on fall thru, XB@-2,Y YB@-1,Y XE@0,Y and YE@1,Y

TFR

D,X

;save XL in high half of X

CLRA

;zero upper half of D

LDAB

0,Y

;D = 0:XE

SUBB

-2,Y

;D = 0:(XE-XB)

EXG

D,X

;X = (XE-XB).. D = XL:junk

SUBA

-2,Y

;A = (XL-XB)

EXG

A,D

;D = 0:(XL-XB), uses trick of EXG

FDIV

;X reg = (XL-XB)/(XE-XB)

EXG

D,X

;move fractional result to A:B

EXG

A,B

;byte swap - need result in B

TSTA

;check for rounding

BPL

NO_ROUND

INCB

;round B up by 1

NO_ROUND

LDAA

1,Y

;YE

PSHA

;put on stack for TBL later

LDAA

-1,Y

;YB

PSHA

;now YB@0,SP and YE@1,SP

TBL

2,SP+

;interpolate and deallocate

;stack temps

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