Compute the effective address and the content of ACC (accumulator) for a load in

Question

Compute the effective address and the content of ACC (accumulator) for a load instruction of a 1-address machine for each type of addressing modes using the following assumptions:

?The load instruction is of length 4 bytes, the first byte is for op ode and mode and the other two bytes contain the value 90 for an address or an immediate value;

? The load instruction is stored in locations 12-15;

?The register (say R1)contains the value 800;

?The location 800 contains the value 700;

?The location 90 contains the value 150;

? The location 150 contains the value 77;

? The location 102 contains the value 11;

? The location 106 contains the value 200;

? The location 890 contains the value 76

Direct

Immediate

Indirect

Relative

Index

Register

Register Indirect

Explanation / Answer

1. Direct ( address 90 is given in instruction)

Effective Address = 90

ACC =value at address 90 = 150

2. Immediate( value and not address is given in the instruction)

ACC = 90

3. Indirect

Effective Address = Address at 90 = 150

ACC =value at address 150 = 77

4. Relative

Effective Address = 90 + bit displacement = 90 + 16 = 106

ACC = value at 106 = 200

5. Index

Effective Address = 102

ACC = value at 102 = 11

6. Register(address is given in register )

Effective Address = 800

ACC = Value at 800 = 700

7. Register Indirect (address = 90 + register contents)

Effective Address = 800 + 90 = 890

ACC = Value at 890 = 76

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