HCS12 datasheet(421/452 Pages) FREESCALE

421 / 452 page

S12CPUV2 Reference Manual, Rev. 4.0

Freescale Semiconductor

421

SP. The branch range is a 9-bit signed value (–512 to +511) which gives

these instructions twice the range of a short branch instruction.

B.8.4 Long Branches

All of the branch instructions from the M68HC11 are also available with

16-bit offsets which allows them to reach any location in the 64-Kbyte

address space.

B.8.5 Minimum and Maximum Instructions

Control programs often need to restrict data values within upper and lower

limits. The CPU12 facilitates this function with 8- and 16-bit versions of MIN

and MAX instructions. Each of these instructions has a version that stores

the result in either the accumulator or in memory.

For example, in a fuzzy logic inference program, rule evaluation consists of

a series of MIN and MAX operations. The min operation is used to

determine the smallest rule input (the running result is held in an

accumulator), and the max operation is used to store the largest rule truth

value (in an accumulator) or the previous fuzzy output value (in a RAM

location) to the fuzzy output in RAM. The following code demonstrates how

MIN and MAX instructions can be used to evaluate a rule with four inputs

and two outputs.

LDY

#OUT1

;Point at first output

LDX

#IN1

;Point at first input value

LDAA

#$FF

;start with largest 8-bit number in A

MINA

1,X+

;A=MIN(A,IN1)

MINA

1,X+

;A=MIN(A,IN2)

MINA

1,X+

;A=MIN(A,IN3)

MINA

1,X+

;A=MIN(A,IN4) so A holds smallest input

MAXM

1,Y+

;OUT1=MAX(A,OUT1) and A is unchanged

MAXM

1,Y+

;OUT1=MAX(A,OUT2) A still has min input

Before this sequence is executed, the fuzzy outputs must be cleared to

zeros (not shown). M68HC11 MIN or MAX operations are performed by

executing a compare followed by a conditional branch around a load or store

operation.

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