Atari 800 Manuel de l'opérateur télécharger pdf (Page 40)

I]]]l

w4)

Th€ appearance of this line on the screen will be different only because the

screen has 38 characters

positions,

while the

printer

has

,10.

BYTE, DBYTE and ['ORD Dir€ctives

100 . BYTE

a,b,...

200 . BYTE

*A,B,...

300 . DBYTE a,b,...

400 .],I/ORD a,b,...

These direciives are similar in ihat they are used to insert data rather than

insiructions into the

proper places

in the

program.

Each directlve is slightly

different in ihe manner in which ii insefts data.

BYTE Directiwe

The BYTD directive reseNes a location

(at

least one) in memory. The directiv€

increments the

program

counter to leave space in memory to be filled by

infor-

mation required by the

prcgram. The

ope.and supplies the data to

go into that

Exampl€s:

1 0 . . . . .

20 , BYTE 34

3 0 . . . . .

Here,

the

Assembler

assembles

into successiv€ locations the instruction of line

10,

then the decimal

nunber

34, then

the insiruciion of line 30.

1 0 . . . . .

20 . BYTE 34, 56,78

3 0 . . . . .

Here, the

Assembter

assembles

inio successiv€ locations the instruction of line

10, then the

decimal

numbers 34, 56

and

78, ihen ihe instruction ofline 30. The

operand may be an expression more complex than the numbers used

the

examples. The rules for writing and evaluating an expression are

given in

App€ndrx D.

10 .....

20 . BYTE

*ATARI"

3 0 . . . . .

Here,

the

Assembler

assembles

inio succ€ssive locaiions ihe instruction ofline

10, ihen ihe

(ATASCII

code) hex numbers a1,54,41,52 and49, then thc instruc

tion of line 30.

DBYIE Directive

The

DBYTE directive

reserves

two

locations {br each expression in the operand.

The

value ofthe expression

assembled

with the high-order bvte first

(in

the

lower numbe. location). For example:

=$4000

20 . nBYTr- ABS

$3000

t w l

when line 20

assembled

and ihe value ofABS

$3000

is deiermined to be

(say)

{,{g/

$5123, $51

put in location

$a000

and

$23

pui

in location

$4001.

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 91 92

Commentaires sur ces manuels

Pas de commentaire

Atari 800 Manuel de l'opérateur Page 40

Commentaires sur ces manuels

Produits connexes et manuels pour PC/postes de travail Atari 800