Motorola M68000 Betriebsanweisung PDF herunterladen (Seite 78)

64 Assembly Language Programming for the 68000 Family

not equal, it is sometimes difficult to remember which value should be

the source and which value should be the destination. The CMP instruc

tion compares the destination with the source. Therefore, if we wish to

determine if DO is less than or equal to D1 we would write

CHP.L DirDO

BLE LABEL

An easy way to remember this is:

destination <inequality> source

The following table shows the conditional branches for signed numbers.

C tA f A

{I < / BLT Branch on less than

f < = /' BLE Branch on less or equal

= BEQ Branch on equal

> = BGE Branch on greater or equal

> BGT Branch on greater than

not = BNE Branch on not equal

When you compare unsigned numbers you should use the following.

< BCS® Branch on carry set

< = BLS Branch on lower or same

= BEQ Branch on equal

> = BCC° Branch on carry clear

> BHI Branch on higher

not = BNE Branch on not equal

0 These mnemonics are not particularly indicative of their function, but they are the

ones to use.

The tests for equal and not equal use the same conditional branches

for both signed and unsigned numbers. The following program finds

the largest unsigned number from an arbitrary number of input values.

Entering a zero value terminates input and outputs the result.

* FIND LARGEST

INPUT VALUE

* ZERO

VALUE TERMINATES INPUT

CLR.L D1

INITIAL VALUE IS ZERO

JSR

INDEC GET NEXT INPUT VAL

TST.L

ZERO?

BEQ FINI

YESr ALL DONE

CMP.L

Dlr DO LARGER?

BLE

1 2 ... 73 74 75 76 77 78 79 80 81 82 83 ... 255 256

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