AMD-K6-2E Datasheet, PDF (42/332 Pages) Advanced Micro Devices – AMD-K6™-2E Embedded Processor

AMD-K6™-2E Processor Data Sheet
Preliminary Information
22529B/0—January 2000
General-Purpose
Registers
31
The eight 32-bit x86 general-purpose registers are used to hold
integer data or memory pointers used by instructions. Table 2
contains a list of the general-purpose registers and the
functions for which they are used.
Table 2. General-Purpose Registers
Register Function
EAX Commonly used as an accumulator
EBX Commonly used as a pointer
ECX Commonly used for counting in loop operations
EDX Commonly used to hold I/O information and to pass parameters
EDI Commonly used as a destination pointer by the ES segment
ESI Commonly used as a source pointer by the DS segment
ESP Used to point to the stack segment
EBP Used to point to data within the stack segment
To support byte and word operations, EAX, EBX, ECX, and
EDX can also be used as 8-bit and 16-bit registers. The shorter
registers are overlaid on the longer ones. For example, the
name of the 16-bit version of EAX is AX (low 16 bits of EAX)
and the 8-bit names for AX are AH (high order bits) and AL (low
order bits). The same naming convention applies to EBX, ECX,
and EDX.
EDI, ESI, ESP, and EBP can be used as smaller 16-bit registers
called DI, SI, SP, and BP respectively, but these registers do not
have 8-bit versions. Figure 7 shows the EAX register with its
name components, and Table 3 on page 25 lists the doubleword
(32-bit) general-purpose registers and their corresponding word
(16-bit) and byte (8-bit) versions.
16 15
87
0
EAX
AX
AH
AL
Figure 7. EAX Register with 16-Bit and 8-Bit Name Components
24
Software Environment
Chapter 3