Intel 8080 - B4_Page_16

Chapter 5. Macros
5-18
The macro call BLOCK 3,LAB generates the following source code:
LAB1:
LAB2:
LAB3:
BLOCK
DB
DB
DB
3,LAB
o
o
o
The assembler controls specified in these two macros (the lines beginning with $) are used to clean up the
assembly listing for easier reading. The source code shown for the
call BLOCK 3,LAB is what appears in the
assembly listing when the controls are used. Without the controls, the assembly listing appears
as follows:
BLOCK 3,LAB
COUNT SET 0
REPT
3
COUNT SET
COUNT+1
INC LAB,%COUNT
ENDM
COUNT SET
COUNT+1
INC LAB,%COUNT
LAB1 : DB 0
COUNT SET
COUNT+l
INC LAB,%COUNT
LA,B2:
DB 0
COUNT SET
COUNT+l
INC
LAB,%COUNT
LAB3: DB
0
Example 3: A Macro that Converts Itself into a Subroutine
In some cases, the in-line coding substituted for each macro call imposes an unacceptable memory requirement.
The next three examples show three different methods for converting a macro
call into a subroutine call. The
first time the
SBMAC macro is called, it generates a full in-line substitution which defines the SUBR subroutine.
Each subsequent call to the SBMAC macro generates only a CALL instruction to the SUBR subroutine.
Within the following examples, notice that the label
SUBR must be global so that it can be called from outside
the first expansion. This
is possible only when that part of the macro definition contai ning the global label is
called only once in the entire program.
Method #1: Nested
Macro Definitions
Macros can be redefined during the course of a program. In the following example, the definition of SBMAC
contains its own redefinition as a nested macro. The first time SBMAC is called, it is full expanded, and the
redefinition of
SBMAC replaces the original definition. The second time SBMAC is called, only its redefinition
(a CALL instruction) is expanded.