Assembler Registers

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TMT Pascal Language Description

Built-in Assembler

Assembler Registers

The following registers can appear in built-in assembler:

8-bit:	AL BL CL DL AH BH CH DH
16-bit:	AX BX CX DX SI DI BP SP
32-bit:	EAX EBX ECX EDX ESI EDI EBP ESP
Segment:	CS DS ES SS FS GS
8087:	ST
Control:	CRn
Debug:	DRn
Test:	TRn

The segment register can be used for segment overrides. 32-bit registers can be used for indexation following the standard 80386 conventions. 16-bit registers should never be used for addressing, unless your entire program does not exceed 64K. Even then,addressing with 16-bit registers is inefficient. Generally, an address is formed as

  Base + Index * Scale + Displacement

where Base is any of the 32-bit registers, Index is any 32-bit register but not ESP, and Scale should be 1,2,4, or 8. Finally, the Displacement is a 32-bit integer quantity.

Here are some valid and invalid indexing modes:

[EAX+EBX]	ok
[EAX+EAX]	ok, EAX is both base and index.
[ESP]	ok, ESP is index, no base.
[EDX*2]	ok, use this to index a global array of words.
[EAX*4+EBP]	ok, use this to index a local array of longints.
[SI]	ok, but is likely to lead to hard-to-find bugs.
[ESI+BX]	illegal, mix of 16- and 32- bit registers.
[SI*4]	illegal, 16-bit registers cannot be scaled.
[ESP*4]	illegal, ESP cannot be an index.

Please consult Intel^™ 80386 programmer's reference for more details.


Opcodes	Table of Content	Opcode Mnemonics

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