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Dear Sir,
I m in beginning phase of 8051 with C. i have compiled my c file and i found in .m51 file that one of the SFR and a user defined variable share the same memory space(0080H) .How it's possible.Could you pls explain me. .M51 lists ....
------- MODULE func1
D:0080H PUBLIC PORT0 I:0080H PUBLIC variabl1
Kindly help with reference to above.
regards, Arup
Yes, it is possible for two variables to have the same address - even in the same Address Space!
This is a result of the Overlaying scheme used by the Keil C51 compiler for Automatic variables (ie, non-static local variables).
But that's not what you're seeing here.
I understood. Thanks to everybody for the quick help.
regards
Arup
dear sir, what i understand is above 007F in internal data memory if my SFR occupies x no of bytes of memory ,then same memory location(numerical) i can use for user defined variables in different addr space i.e IDATA
correct me if wrong.
thanks, Arup
what i understand is above 007F in internal data memory if my SFR occupies x no of bytes of memory ,then same memory location(numerical) i can use for user defined variables in different addr space i.e IDATA
DO read 'the bible'
while your statement abobe is basically correct there is no such thing as my SFR and no SFR "occupies x no of bytes", they all 'occupy' ONE.
I do appreciate, that your expressions may be due to 'language', but if you had (as you MUST) studied 'the bible' I am sure that the language woul have been clearer.
Erik
what i understand is above 007F in internal data memory if my SFR occupies x no of bytes of memory ,then same memory location(numerical) i can use for user defined variables in different addr space i.e IDATA<p>
The SFR area contains 128 bytes. What SFRs these 128 bytes contain, and at which address, mostly depends on the type of chip you are using. The chip documentation will provide this information.
Whether your chip also has 128 of (indirectly addressable) RAM starting at address 0x80 also depends on what chip you are working with. Information about this will also be in the chips documentation.
If your chip has the 128 bytes of RAM at address 0x80, then they will be usable as part of the IDATA space.
(IDATA refers to all internal RAM that is indirectly addressable, which means that it ranges from 0x00 to 0xFF. Be aware that the low addresses also contain the register space and the bit-adressable area.
DATA refers to directly addressable internal RAM, which means 0x00 to 0x7F).
"there is no such thing as my SFR"
True for a standard chip, but (possibly) not if you're using a softcore, or something like the old Triscend...
" no SFR 'occupies x no of bytes', they all 'occupy' ONE."
The so-called "bible" refers to the (TH0+TL0) and (TH1+TL1) pairs as "16-bit registers"
DPTR is also a 16-bit register (thought also accessible as DPH and DPL)
There maybe others specific to particular derivatives?