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before we continue ... allow me to show you short theory about General
Purpose Register
... since u will deal with them in every steps ...... |
| -
Accumulator : EAX (32 bit) Extended of AX (16 bit).
AX split into two 8 bit registers : AH (Acc high) & AL (Acc low) |
| use for arithmetic and logical computations |
| -
Base : EBX (32 bit) Extended of BX (16 bit).
BX split into two 8 bit registers : BH (Base high) & BL (Base low) |
| hold indirect addresses |
| -
Count : ECX (32 bit) Extended of CX (16 bit).
CX split into two 8 bit registers : CH (Count high) & CL (Count low) |
| to count off the number of iterations in a loop or specify the number of characters in a string. |
| -
Data : EDX (32 bit) Extended of DX (16 bit).
DX split into two 8 bit registers : DH (Data high) & DL (Data low) |
| holds
the overflow from certain arithmetic operations, and it holds I/O addresses
when
accessing data on the I/O bus. |
| - Source Index : ESI (32 bit) Extended of SI (16 bit) |
| use
as pointers (much like the bx register) to indirectly access memory. Youll
also use these
registers with the string instructions when processing character strings. This is a pointer within a segment (usually DS) that is read from by the CPU. |
| - Destination Index : EDI (32 bit) Extended of DI (16 bit) |
| use
as pointers (much like the bx register) to indirectly access memory. Youll
also use these
registers with the string instructions when processing character strings. This is a pointer within a segment (usually ES) that is written to by the CPU. |
| - Base Pointer : EBP (32 bit) Extended of BP (16 bit) ; similiar to Base Register |
| use to access parameters and local variables in a procedure. |
| - Stack Pointer : ESP (32 bit) Extended of SP (16 bit) |
| maintains
the program stack. Normally, you would not use this register for arithmetic
computations. The proper operation of most programs depends upon the careful use of this register. |
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| Note
that the eight bit registers do not form an independent register set. Modifying
al will change the
value of ax; so will modifying ah. The value of al exactly corresponds
to bits zero through seven of ax. The value of ah corresponds to bits eight
through fifteen of ax. Therefore any modification
to al or ah will modify the value of ax. Likewise, modifying ax will change
both al and ah. Note, however, that changing al will not affect the value
of ah, and vice versa.
This statement
applies to bx/bl/bh, cx/cl/ch, and dx/dl/dh as well. The si, di, bp, and
sp registers
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