Keil Software — A51/AX51/A251 Macro Assembler and Utilities |
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Memory Initialization
The memory initialization directives are used to initialize code or constant space in either word, double-word, or byte units. The memory image starts at the point indicated by the current value of the location counter in the currently active segment.
DB
The DB directive initializes code memory with 8-bit byte values. The DB directive has the following format:
label: |
DB expression |
, expression … |
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label |
is the symbol that is given the address of the initialized |
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memory. |
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expression is a byte value. Each expression may be a symbol, a character string, or an expression.
The DB directive can only be specified within a code or const segment. If the DB directive is used in a different segment, Ax51 will generate an error message.
Example
REQUEST: |
DB |
'PRESS ANY KEY TO CONTINUE', 0 |
TABLE: |
DB |
0,1,8,'A','0', LOW(TABLE),';' |
ZERO: |
DB |
0, '''' |
CASE_TAB: |
DB |
LOW(REQUEST), LOW(TABLE), LOW(ZERO) |
Shaded directives and options are available only in AX51 and A251.
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Chapter 4. Assembler Directives |
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DW
The DW directive initializes code memory with 16-bit word values. The DW directive has the following format:
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label: |
DW |
expression , expression … |
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where |
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label |
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is the symbol that is given the address of the initialized |
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memory. |
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expression |
is the initialization data. Each expression may contain a |
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symbol, a character string, or an expression. |
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The DW directive can only be specified within a code or const segment. If the |
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DW directive is used in a different segment, Ax51 will generate an error |
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Examplemessage. |
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TABLE: |
DW |
TABLE, TABLE + 10, ZERO |
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ZERO: |
DW |
0 |
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CASE_TAB: |
DW |
CASE0, CASE1, CASE2, CASE3, CASE4 |
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DW |
$ |
Shaded directives and options are available only in AX51 and A251.
Keil Software — A51/AX51/A251 Macro Assembler and Utilities |
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DD (AX51 & A251 only)
The DD directive initializes code memory with 32–bit double word values. The DD directive has the following format:
label: DD |
expression , expression … |
where |
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label |
is the symbol that is given the address of the initialized |
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memory and |
expression |
is the initialization data. Each expression may contain a |
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symbol, a character string, or an expression. |
The DD directive can only be specified within a code or const segment. If the DD directive is used in a different segment, Ax51 will generate an error message.
Example |
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TABLE: |
DD |
TABLE, TABLE + 10, ZERO |
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DD |
$ |
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ZERO: |
DD |
0 |
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LONG_VAL: |
DD |
12345678H, 0FFFFFFFFH, 1 |
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Shaded directives and options are available only in AX51 and A251.