ADDRESSING MODES Consider an instruction. The address field of the instruction c

Question

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 2000 1600 2500 3000 3600 Memory Content 844 3000 400 800 1200 500 For each of the Addressing Modes, specify the Effective (Target) Address and value found at that address. For each case qive a brief explanation. Effective Address (bvtes Value Addressing Modes IMMEDIATE DIRECT INDIRECT REGISTER REGISTER INDIRECT DISPLACEMENT

Explanation / Answer

VALUE

ADDRESSING MODE EXPLAINATION EFFECTIVE ADDRESS

VALUE

IMMEDIATE The specified address is the operand iteself. NIL   2000 DIRECT The specified address holds the operand. 2000 3000 INDIRECT The specified address is the address which holds the operand. 3000 1200 REGISTER The value at the specified address is the operand. NIL   1600 REGISTER INDIRECT The value of the specified register is the memory address of the operand. 1600 400 DISPLACEMENT In the specified address, a constant value is added that can either be explicitly stated or in this case, that constant is register's value. Therefore effective address=2000+1600. 3600 500

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