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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

Parents
  • 0 in reply to Mark Odell

    Yes, and you use sbit, sfr, sfr16 to access them. Assembler allows you to do anything so I'll ignore that here.

    When you do it in Assembler, you choose the appropriate Addressing Mode and/or mnemonic yourself; it's the sbit, sfr, sfr16 which tell the compiler that you're accessing an SFR and therefore what Addressing Mode and/or mnemonic to use.

Reply
  • 0 in reply to Mark Odell

    Yes, and you use sbit, sfr, sfr16 to access them. Assembler allows you to do anything so I'll ignore that here.

    When you do it in Assembler, you choose the appropriate Addressing Mode and/or mnemonic yourself; it's the sbit, sfr, sfr16 which tell the compiler that you're accessing an SFR and therefore what Addressing Mode and/or mnemonic to use.

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