Page 151 - Introduction to Microcontrollers Architecture, Programming, and Interfacing of The Motorola 68HC12

128 Chapter 5 Advanced Assemblers, Linkers, and Downloaders

Table 5.5. Macro Arguments

Every time the programmer uses this macro, he or she writes

label name parameter,parameter,...,parameter
where name is the name of the macro, which is placed in the operation field, to which
an optional size . B, .W,or .L may be appended. The designation label at the
beginning of the line is treated just like a label in front of a conventional assembly line.
The parameters can be inserted into the body of the macro using the two-character
symbols in Table 5.5. As an example, the macro
MOVE: MACRO
LDD \1
STD \2
ENDM
will move the two bytes at parameter location \1 to parameter location \2, like the MOW
instruction, but the macro is faster and shorter where the second parameter is a page-zero
address. When used in the program, say as
MOVE Z+3,M (1)
the two bytes at locations Z + 3, Z + 4 will be moved to locations M, M + 1. In this
example, all the usual rules for choosing between direct and page-zero addressing would
apply. Additionally, if the actual parameters involve an index mode of addressing that
uses a comma, the actual parameters must be enclosed within parentheses as in MOVE
( 3, X) , Y for the sequence
LDD 3, X
STD Y

As implied in the example above, when a macro is used, the actual parameters are
inserted in a one-to-one correspondence with the order in (1).
If "goto" labels are to be used within macros, then, because the macro may be used
more than once during the program, assembler-generated labels must be used. The
symbol character pair "\@" means an underbar followed by the macro invocation number,
which is initially zero and is incremented each time a macro is called. When the first
macro is expanded \@ generates the label _00000, when the second macro is expanded,
\@ generates _00001, and so on. Throughout the first macro, \@ generates _00000 even
though this macro may call another macro expansion, whenever it is used, before or after
other macros are called and expanded. This generated symbol can be concatenated to other