LGS - Load Far Pointer Instruction

The LGS instruction is used to load (read) a segment and address from memory into registers. The memory address most hold the Segment and offset address.

This command has 3 parts, Instruction, Register, and a 32 bit memory address made up of 16 bit Segment number followed by an offset from the start of it.

LGS loads the Offset address into the Register provided in the first operand, then the Segment in to the GS Register

Breakdown Description 16 bit Machine
Code

LGS ; Instruction 0F B5

SI ; Register number

[BX] ; A memory address from [BX]
; pointed to by BX

DataAddress ; A Label address 25 C0

LGS using a memory address

Assembly
Sample Description

MOV BX, 0x0345 ; Assign the memory address of the Pointer

or

MOV BX, DataAddress ; Assign the memory address of the Pointer

LGS SI, [BX] ; Call LGS

Alternate method

Assembly
Sample Description

MOV BX, 0x0005 ; Assign the memory address of the Pointer

PUSH BX

POP GS

MOV SI, DataAddress ; Assign the memory address of the Pointer
; to a Register

Assembly
Sample Description 16 bit Machine
Code

LGS SI, [BX] ; Load GS and a Register from
; the memory adress in [BX] 0F B5 33

Breakdown	Description	16 bit Machine Code
LGS	; Instruction	0F B5
SI	; Register number
[BX]	; A memory address from [BX] ; pointed to by BX
DataAddress	; A Label address	25 C0

Assembly Sample	Description
MOV BX, 0x0345	; Assign the memory address of the Pointer
or
MOV BX, DataAddress	; Assign the memory address of the Pointer
LGS SI, [BX]	; Call LGS

Assembly Sample	Description
MOV BX, 0x0005	; Assign the memory address of the Pointer
PUSH BX
POP GS
MOV SI, DataAddress	; Assign the memory address of the Pointer ; to a Register