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Appendix D. Assembler Differences
This appendix lists the differences between the Intel ASM-51 assembler, the
Keil A51 assembler, and the Keil A251/AX51 assembler.
Differences Between A51 and A251/AX51
Assembly modules written for the A51 assembler may be assembled using the A251/AX51 macro assembler. However, since the A251 macro assembler supports the Intel/Atmel WM 251 architecture and the AX51 macro assembler supports extended 8051 variants like the Philips 80C51MX, the following incompatibilities may arise when A51 assembly modules are assembled with the A251/AX51 assembler.
32-Bit Values in Numeric Evaluations |
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The A51 assembler uses 16-bit values for all numerical expressions. The |
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A251/AX51 macro assembler uses 32-bit values. This may cause problems |
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when overflows occur in numerical expressions. For example: |
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Value |
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generates the result 800h in A51 since the result of the addition is only a 16-bit value (1000h). However, the A251/AX51 assembler calculates a value of 8800h.
8051 Pre-defined Special Function Register Symbol Set
The default setting of the A51 assembler pre-defines the Special Function Register (SFR) set of 8051 CPU. This default SFR set can be disabled with the A51 control NOMOD51. Both A251 and AX51 do not pre-define the 8051 SFR set. The control NOMOD51 is accepted by A251/AX51 but does not influence any SFR definitions.
More Reserved Symbols
The A251/AX51 macro assembler has more reserved symbols as A51. Therefore it might be necessary to change user-defined symbol names. For example the symbol ECALL cannot be used as label name in A251/AX51, since it is a mnemonic for a new instruction.
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Appendix D. Assembler Differences |
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Object File Differences |
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Ax51 uses the OMF-251/51MX file format for object files. A51 uses an |
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extended version of the Intel OMF-51 file format. The OMF-51 file format |
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limits the numbers of external symbols and segments to 256 per module. The |
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OMF-251 file format does not have such a limit on the segment and external |
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declarations. |
Differences between A51 and ASM51
Assembly modules written for the Intel ASM51 macro assembler can be re-translated with the A51 macro assembler. However you have to take care about the following differences:
Enable the MPL Macro Language
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need to be enable with the MPL control. |
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The Intel ASM51 pre-defines the following symbol names if MOD51 is |
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active: RESET, EXTI0, EXTI1, SINT, TIMER0, TIMER1. A51 does not |
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pre-define this symbol names. |
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More Reserved Symbols |
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Since the A51 macro assembler supports also conditional assembly and |
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standard macros, A51 has more reserved symbols then Intel ASM51. |
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Therefore it might be necessary to change user-defined symbol names. For |
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example the symbol IF cannot be used as label name in A51, since it is a |
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control for conditional assembly. |
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Object File Differences |
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The A51 assembler generates line number information for source level |
debugging and file dependencies. For compatibility to previous A51 versions and to ASM51, the line number information can be disabled with the A51 control NOLINES.
C Preprocessor Side Effects
The integrated C preprocessor in Ax51 has two side effects that are incompatible to the Intel ASM51 macro assembler. If you are using the backslash character at the end of a comment line, the next line will be comment out too. If you are using $INCLUDE in conditional assembly blocks, the file must exist even when the block will not be assembled.
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Differences between A251/AX51 & ASM51
Assembly modules written for Intel ASM51 can be re-translated with the A251 macro assembler. However, since the A251 macro assembler supports additional 251 features, the following incompatibilities can arise when ASM51 modules are re-translated with A251.
32-Bit Values in Numeric Evaluations
The ASM51 assembler uses 16-bit numbers for all numerical expressions. The A251 macro assembler uses 32-bit values. This can cause problems when overflows occur in numerical expressions. For example:
Value |
EQU |
(8000H + 9000H) / 2 |
has the result 800H in ASM51 since the result of the addition is only a 16-bit value (1000H), whereas the A251 calculates Value as 8800H.
8051 Pre-defined Symbols
The default setting of Intel ASM51 pre-defines the Special Function Register D (SFR) set and symbol names for reset and interrupt vectors of 8051 CPU.
This default symbol set can be disabled with the ASM51 control NOMOD51. A251 does not pre-define any of the 8051 SFR or interrupt vector symbols. The control NOMOD51 is accepted by A251 but does not influence any symbol definitions.
More Reserved Symbols
The A251 macro assembler has more reserved symbols as ASM51. Therefore it might be necessary to change user-defined symbol names. For example the symbol ECALL cannot be used as label name in A251, since the Intel/Atmel WM 251 has a new instruction with that mnemonic.
Enable the MPL Macro Language
If your assembly module contains Intel ASM51 macros, the A251 MPL macros need to be enabled with the MPL control.
Object File Differences
The A251 assembler uses the Intel OMF-251 file format for object files. The ASM51 assembler uses the Intel OMF-51 file format. The OMF-51 file format limits the numbers of external symbols and segments to 256 per module. The OMF-251 file format does not have such a limit on the segment and external declarations. The ASM51 assembler generates line number information for source level debugging. For compatibility with ASM51, line number information can be disabled with the A251 control NOLINES.
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C Preprocessor Side Effects
The integrated C preprocessor in Ax51 has two side effects that are incompatible to the Intel ASM51 macro assembler. If you are using the backslash character at the end of a comment line, the next line will be comment out too. If you are using $INCLUDE in conditional assembly blocks, the file must exist even when the block will not be assembled.
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