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yu zhou

code segment:

              ...
        EXTRN   NUMBER (MAX_NUM)


        DS      MAX_NUM


        END

another code segment:

        PUBLIC  MAX_NUM
        MAX_NUM EQU     8

when i assembled and linked these codes,
there was an error:

        Build target 'test'
assembling test.asm...
test.asm(13): error A28: ABSOLUTE EXPRESSION REQUIRED
Target not created

How did it hanppen?

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  • 0 in reply to yu zhou

    They work in assembly, but for runtime variables - variables that gets a memory address. The linker must be able to know how to get a reference from one source code module to be able to use a variable that exists in another module.

    But this is separate from assembly-time numeric constants used by the assembler. EQU does not produce a runtime variable. There will be no memory allocated in the RAM of the microcontroller for an EQU symbol. And since it is an assembly time constant without a memory address, there will be no need/use for any EXTRN/PUBLIC to inform the linker about the constant. Without a memory address to share between multiple source modules, the linker don't need to know.

    But all this is introductory stuff, and as I have already mentioned, the same concept exists for C also. Get a good introductory book about assembly programming.

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  • 0 in reply to yu zhou

    They work in assembly, but for runtime variables - variables that gets a memory address. The linker must be able to know how to get a reference from one source code module to be able to use a variable that exists in another module.

    But this is separate from assembly-time numeric constants used by the assembler. EQU does not produce a runtime variable. There will be no memory allocated in the RAM of the microcontroller for an EQU symbol. And since it is an assembly time constant without a memory address, there will be no need/use for any EXTRN/PUBLIC to inform the linker about the constant. Without a memory address to share between multiple source modules, the linker don't need to know.

    But all this is introductory stuff, and as I have already mentioned, the same concept exists for C also. Get a good introductory book about assembly programming.

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