Cirrus Logic CS485 Manual de usuario descargar pdf (Pagina 13)

CS485G Spring 2015 13

3. Registers

32-bit 16-bit 8-bit original purpose

eax ax ah/al accumulator

ebx bx bh/bl base

ecx cx ch/cl counter

edx dx dh/dl data

esi source index

edi destination index

esp sp stack pointer

ebp bp base pointer

4. Moving data: mov1 source dest

5. Operand types

(a) Immediate: integer constant, such as $0x400 or $-533 The

actual constant is represented in 1, 2, or 4 bytes, depending on

size; the assembler chooses the right representation. The source

may be immediate, but not the destination.

(b) Register: any of the 8 integer registers, such as: %ecx (although

%esp and %ebp have special purposes). Either source or desti-

nation or both may be register.

(d) Memory: 4 bytes of memory whose ﬁrst byte is addressed by

any register, such as (%eax) (note the parentheses). Either source

or destination, but not both, may be memory.

(e) Displacement: 4 bytes of memory whose ﬁrst byte is addressed

by any register plus some constant, such as 8(%eax). Either

source or destination, but not both, may be memory or displace-

ment.

6. Example in C: Swap

1 void swap(int

xp, int

yp)

2 {

3 int t0 =

xp;

4 int t1 =

yp;

xp = t1;

yp = t0;

7 }

7. Same thing in assembler

1 2 ... 8 9 10 11 12 13 14 15 16 17 18 ... 66 67

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Cirrus Logic CS485 Manual de usuario Pagina 13