Chapter
5. Macros
The assembler must encounter the macro definition before the first
call
for that macro. Otherwise, the macro
call
is
assumed to
be
an
illegal
opcode. The assembler inserts the macro body identified
by
the macro name
each time
it
encounters a
call
to a previously defined macro
in
your program.
The positioning
of
actual parameters
in
a macro
call
is
critical since the substitution of parameters
is
based
solely on position. The first-listed actual parameter replaces each occurrence of the first-listed dummy param-
eter; the second actual parameter replaces the second dummy parameter, and
so
on.
When
coding a macro call,
you must
be
certain to list actual parameters
in
the appropriate sequence for the macro.
Notice that blanks are usually treated
as
delimiters. Therefore, when
an
actual parameter contains blanks
(passing the instruction
MOY
A,M,
for example) the parameter must
be
enclosed
in
angle brackets. This
is
also
true for any other delimiter that
is
to
be
passed
as
part
of
an
actual parameter. Carriage returns cannot
be
passed
as
actual parameters.
If a macro call specifies more actual parameters than are listed
in
the macro definition, the extra parameters
are ignored.
If
fewer parameters appear
in
the
call
than
in
the definition, a null replaces each missing parameter.
Example:
The following example shows two calls for the macro
LOAD.
LOAD
is
defined
as
follows:
LOAD
MACRO
Gl,G2,G3
LOCAL
MOYES
MOYES:
LHLD
Gl
MOY
A,M
LHLD
G2
MOY
B,M
LHLD
G3
MOY
C,M
ENDM
LOAD
simply loads the accumulator with a byte of data from the location specified
by
the first actual parameter,
the B register with a byte from the second parameter, and the
C register with a byte from the third parameter.
The first time
LOAD
is
called,
it
is
used
as
part of a routine that inverts the order of three bytes
in
memory.
The second time
LOAD
is
called, it
is
part of a routine that adds the contents
of
the B register to the accumu-
lator and then compares the result with the contents of the C register.
5-13
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