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SFR access without keyword "sfr"

Arnaud DELEULE

Hi,

I'm trying to access SFR memory using the hexa address of the SFR
and using only "C" instructions.
Since SFR memory is accessed by direct addressing mode, like the first
128 bytes of internal RAM, I tried to use the following instruction :

* ((unsigned char data *) 0xA8) = 0x1;
Unfortunately the generated code is :
MOV  	R0,#0A8H
MOV  	@R0,#01H
which is indirect addressing and points to the upper 128 bytes of
internal memory (in a 8052) or nowhere (with 8051).

If I try to address specificly the upper 128 bytes of internal RAM using
* ((unsigned char idata *) 0xA8) = 0x1;
then the generated code is :
MOV  	R0,#0A8H
MOV  	@R0,#01H
which seems to be correct.

I think I miss something but I don't see what.
Anybody can help ?

Thanks in advance.

Arnaud

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  • 0

    you can use the sfr keyword in "C" and it seems the easiest method to use?
    There is the _at_ keyword for absolute memory locations which should do the same (p71 C51 manual). if its only a bit, then sbit can be pointed to a sfr location. ( sbit VAR = 0xA8 )

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  • 0

    you can use the sfr keyword in "C" and it seems the easiest method to use?
    There is the _at_ keyword for absolute memory locations which should do the same (p71 C51 manual). if its only a bit, then sbit can be pointed to a sfr location. ( sbit VAR = 0xA8 )

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