I am studying for an exam, can someone help me understand the question below? Pl

Question

I am studying for an exam, can someone help me understand the question below? Please help me understand what each of the addressing modes below does, and step by step instructions on how the Effective address and values for each are determined

ADDRESSING MODES Consider an instruction. The address field of the instruction contains the value 2000. When needed, register #18 is used. Register 18 contains value 1600 The list below shows a few addresses and the memory content of each of these addresses Address (bytes) 48 Memory Content 844 600 For each of the Addressing Modes, specify the Effective (Target) Address and value found at that address. For each case give a brief explanation. Addressing Modes Effective Address (bytes Value DIRECT REGISTER INDIREC DISPLACEMENT

Explanation / Answer

1. Immediate Mode: The operand is an immediate value is stored explicitly in the instruction.

so operand value is 2000.

EA is the location of this instruction. (not mentioned in the question)

2.Direct Mode: The instruction specify the direct address of the operand.

EA is 2000 and operand value is 3000

3. Indirect Mode: The instruction specify the indirect address where the effective address of the operand is stored.

As instruction contain 2000. so EA is 3000 and operand value is 1200.

4. Register Mode: Here operand is in the register. so no memory location.

EA: Nil

Operand: 1600

5. Register Indirect Mode: Here register contains EA of the operand.

EA: 1600

Operand: 400

6. Displacement Mode: it is a combination of direct addressing or register indirect addressing mode.

EA=A+(R)

so here EA : 2000+1600= 3600

Operand: 500

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