Chapter
2.
Assembly
Language
Concepts
Alphanumeric characters include the letters
of
the alphabet, the question mark character, and the decimal
digits
0 through 9.
A name
is
required for the SET, EQU, and MACRO directives. Names follow the same coding rules as labels,
except
that
they must
be
terminated with a blank rather than a colon. The label/name field must be
empty
for
the
LOCAL and
EN
OM
directives.
Opcode Field
This required field contains the mnemonic operation code for the
8080/8085
instruction or assembler directive
to
be
perfor med.
Operand Field
The operand field identifies the data to
be
operated on by the specified opcode. Some instructions require no
operands.
Others require one or two operands.
As
a general rule, when two operands are required (as
in
data
transfer and arithmetic operations), the
fir,t operand identifies the destination (or target) of the operation's
result, and the second operand specifies the ',ource data.
Examples:
MOV
MVI
A,C
A,'B'
;MOVE CONTENTS
OF
REC;
C TO ACCUMULATOR
;MOVE
B TO ACCUMULATOR
Comment
Field
The optional
comment
field may contain an'! information you deem useful for annotating your program. The
only coding requirement for this field
is
that
it
be
preceded
by
a semicolon. Because the ,emicolon i, a delimiter,
there
is
no
need to separate the
comment
from the previous field with one or more
space,>.
However, spaces are
commonly used to improve the readability
of
the
comment.
Although comments arc alway, optional, you should
usc them
liberally since
it
is
easier to debug and maintain a
well
documented
program.
CODING OPERAND
FIELD
INFORMATION
2-4
There are four types
of
information
(a
through d
in
the following list)
that
may
be
requested
as
items
in
the
operand field;
the information may
be
specified
in
nine ways, each
of
which
is
described below.
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