What are SI and DI in 8086?

4 Answers. When you are using instructions like movsb, si is considered as the source register, while di is considered as the destination register. But they are both normal x86 registers. My assembly is a bit rusty, but one’s the Source Index, the other the Destination Index.

What is MOV si?

mov si,es:[bx] Direct Memory Addressing. A memory location can be used by using its address as the operand in an instruction. example: mov ax,aDigit. Register Indirect Addressing.

What is the purpose of MOV instruction?

The mov instruction copies the data item referred to by its second operand (i.e. register contents, memory contents, or a constant value) into the location referred to by its first operand (i.e. a register or memory).

What is the use of SI DI?

SI is called source index and DI is destination index. As the name follows, SI is always pointed to the source array and DI is always pointed to the destination. This is usually used to move a block of data, such as records (or structures) and arrays.

How SI and DI are used respectively?

The SI and DI registers are typically used implicitly as the source and destination pointers, respectively. Unlike the data registers, the pointer/index registers are only accessible as full 16-bit registers.

What is the addressing mode of mov ax Si?

The mode of addressing is known as register indirect mode. In this addressing mode, the offset address of data is in either BX or SI or DI Register. The default segment is either DS or ES. Example: MOV AX, [BX].

What is description of instruction MOV A 40H?

MOV A, 40H Move byte from direct address. to accumulator.

What is MOV BX?

A constant is an immediate operand. MOV AX, 5 ; moves the numeric value 5 into AX MOV AX, @DATA ; moves the constant represented by @data into AX. Direct Operands. A variable name that represents a memory address is a direct (memory) operand. MOV BX, NUM ; moves the contents of the memory variable ; NUM into AX.