156 Chapter 5. Assembler Macros
The following code shows how to invoke the DELAY macro from an assembly program.
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LOOP: |
MOV |
P0, #0 |
;clr PORT 0 |
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DELAY |
5 |
;wait 5 |
NOPs |
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MOV |
P0, #0ffh |
;set PORT 0 |
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DELAY |
5 |
;wait 5 |
NOPs |
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JMP |
LOOP |
;repeat |
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In this example, a value of 0 is written to port 0. The DELAY macro is then invoked with the parameter 5. This will cause 5 NOP instructions to be inserted into the program. A value of 0FFh is written to port 0 and the DELAY macro is invoked again. The program then repeats.
C Macros
The Ax51 macro assembler has a standard C macro preprocessor that is almost identical with the macro preprocessors in the Cx51 compiler. This allows you to
5 use common header files with constant definitions that can be used in assembler and C source files. The Ax51 macro assembler accepts also the special function register directives from the Cx51 compiler. Therefore you may use the same SFR register definition files for both assembler and C source files.
NOTE
C Macros are not available if you have enabled the Intel ASM-51 compatible MPL macro language with the MPL assembler control.
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C Macro Preprocessor Directives
C macro preprocessor directives must be the first non-whitespace text specified on a line. All directives are prefixed with the pound or number-sign character (‘#’). For example:
#include <reg51f.h> #if TEST
#define DEBUG 1 #endif
The following table lists the preprocessor directives and gives a brief description of each.
Directive Description
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define |
Defines a preprocessor macro or constant. |
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elif |
Initiates an alternative branch of the if condition, when the previous if, ifdef, ifndef, |
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or elif branch was not taken. |
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else |
Initiates an alternative branch when the previous if, ifdef, or ifndef branch was not |
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taken. |
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endif |
Ends an if, ifdef, ifndef, elif, or else block. |
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error |
Outputs an error message defined by the user. This directive instructs the |
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compiler to emit the specified error message. |
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ifdef |
Evaluates an expression for conditional compilation. The argument to be evaluated |
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is the name of a definition. |
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ifndef |
Same as ifdef but the evaluation succeeds if the definition is not defined. |
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if |
Evaluates an expression for conditional compilation. |
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include |
Reads source text from an external file. The notation sequence determines the |
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search sequence of the included files. Ax51 searches for include files specified |
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with less-than/greater-than symbols (‘<’ ‘>’) in the include file folder. The include |
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file folder is specified with the INCDIR assembler control and with the environment |
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variable C51INC and is therefore compatible with the Cx51 compiler. Ax51 |
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searches for include files specified with double-quotes (“ “) in the current folder, |
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which is typically the folder of the project file. |
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line |
Specifies a line number together with an optional filename. These specifications |
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are used in error messages to identify the error position. |
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pragma |
Allows you to specify assembler controls and are converted into Ax51 control lines. |
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Refer to “Assembler Controls” on page 197 for more information. |
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undef |
Deletes a preprocessor macro or constant definition. |
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158 |
Chapter 5. Assembler Macros |
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Stringize Operator
The stringize or number-sign operator (‘#’), when used within a macro definition, converts a macro parameter into a string constant. This operator may be used only in a macro that has a specified argument or parameter list.
When the stringize operator immediately precedes the name of one of the macro parameters, the parameter passed to the macro is enclosed within quotation marks and is treated as a string literal. For example:
#define stringer(x) DB #x, 0x0D, 0x0A
stringer (text)
results in the following actual output from the preprocessor.
DB "text", 0x0D, 0x0A
NOTES
The Ax51 macro assembler does not accept C escape sequences like "\n", "\r" or "\x0d". You need to replace these characters with hex values.
Unlike the Cx51 compiler, multiple strings are not concatenated to a single 5 string by the Ax51 macro assembler. Therefore you need to separate multiple
items with a comma when using the Ax51 macro assembler.
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Token-pasting Operator
The token-pasting operator (##) within a macro definition combines two arguments. It permits two separate tokens in the macro definition to be joined into a single token.
If the name of a macro parameter used in the macro definition is immediately preceded or followed by the token-pasting operator, the macro parameter and the token-pasting operator are replaced by the value of the passed parameter. Text that is adjacent to the token-pasting operator that is not the name of a macro parameter is not affected. For example:
TEST1 EQU 0x10
TEST2 EQU 0x20
#define paster(n) DB TEST##n
paster (2)
results in the following actual output from the preprocessor.
DB TEST2
5