- 1 year ago
Indexing Modes Of Turbo Assembler
In Turbo Assembler (TASM), which is a popular assembler for the x86 architecture, there are two main indexing modes: base-relative indexing and based-indexed with displacement.
Base-Relative Indexing:
In base-relative indexing, memory operands are calculated based on a base address. The syntax for base-relative indexing is:csharp[base + offset]
Here,
base
is a base address in a segment, andoffset
is an optional constant displacement. The assembler calculates the effective address by adding the base and offset values.Example:
assemblymov ax, [bx] ; Load the word at the address pointed to by BX into AX
mov al, [si + 5] ; Load the byte at the address pointed to by SI + 5 into AL
Based-Indexed with Displacement:
In this mode, memory operands are calculated based on a base address and an index register. The syntax for based-indexed with displacement is:csharp[base + index + offset]
Here,
base
is a base address,index
is an index register (usually SI or DI), andoffset
is an optional constant displacement. The assembler calculates the effective address by adding the base, index, and offset values.Example:
assemblymov ax, [bx + si] ; Load the word at the address pointed to by BX + SI into AX
mov al, [bx + si + 5] ; Load the byte at the address pointed to by BX + SI + 5 into AL
Both indexing modes are useful for accessing memory locations in various data structures and arrays. The choice of which indexing mode to use depends on the specific requirements of the program and the memory layout of the data. Assembler programmers need to carefully manage the values in the base, index, and offset registers to ensure correct memory access and efficient code execution.