An instruction is stored at location 500 with its address field at location…
2019
An instruction is stored at location 500 with its address field at location 501. The address field has the value 400. A processor register 𝑅1 contains the number 200. Match the addressing mode (List – I) given below with effective address (List-II) for the given instruction:
Choose the correct option from those given below:
- A.
\((a)-(iii), (b)-(i), (c) -(iv), (d)-(ii) \) - B.
\((a)-(i), (b)-(ii), (c) -(iii), (d)-(iv) \) - C.
\((a)-(iv), (b)-(ii), (c) -(iii), (d)-(i) \) - D.
\((a)-(iv), (b)-(iii), (c) -(ii), (d)-(i)\)
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Correct answer: A
Given:
Instruction is at memory location 500; its address field is at location 501 and contains the value 400.
Register R1 contains 200.
After fetching the instruction and its address field, the program counter (PC) points to the next location 502.
Compute effective addresses for each addressing mode:
Direct addressing: use the address field value directly, so EA = 400.
Register indirect: use the contents of R1 as the address, so EA = 200.
Index with R1: add the address field and R1, so EA = 400 + 200 = 600.
Relative addressing: add the address field (offset) to the PC. With PC = 502, EA = 502 + 400 = 902.
Final correct mapping (addressing mode -> effective address):
Direct -> 400
Register indirect -> 200
Index with R1 -> 600
Relative -> 902
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