GATE Computer Science Engineering(CSE) 2027 Test: Addressing Modes- 1 Free

Regs[R₄] ← Regs[R₄] + Regs[R₃] - Register.
Register addressing mode includes every instruction from processor register, I/O device, or a memory location as an operand.

Regs[R₄] ← Regs[R₄] + 3 - Immediate.
In the immediate addressing mode in the instruction, the value of the operands is mentioned explicitly.

Regs[R₄] ← Regs[R₄] + Mem[100] + Regs[R₁] - Displacement.
In the displacement modes, operands are formed of the address by adding the content of the displacement into the base register.

Program counter is the register which keeps track of the execution of a program and which contains the memory address of the instruction which is to be executed next by the processor.

In a vectored interrupt, the source that interrupts supplies the branch information to the computer. This information is called the interrupt vector. In. some computers the interrupt vector is an address that points to a location in memory where the beginning address of the Input Output service routine is stored.

The operation code specifies one of eight input output instructions: Start input/output, start input/ output fast release, test input/output, clear input/ output, halt input/output, halt device, test channel and store channel identification.

3 address instruction:
Two operand locations and a result location are explicitly contained in the instruction word, 
e.g, Y = A - B
2 address instruction:
One of the addresses is used to specify both an operand and the result location,
e.g, Y = Y + X
1 address instruction:
Two addresses are implied in the instruction and accumulator based operations, 
e.g. ACC = ACC + X
0 address instructions:
They are applicable to a special memory organization called a stack. It interact with a stack using push and pop operations. All addresses are implied as in register based operations
T = Top ( T - 1 )

The Jump instruction is at address 3010 H and instruction is 2 bytes. Therefore, PC points to 3012 H on execution of this instruction.
Now Branch Target PC
= PC + (-7)
= 3012 H - 7 H = 3005 H

The address reference is not absolute, it is relative to current location and therefore .these programs are easy to relocate in the memory of the computer.

Immediate addressing modes can be used for either loading internal register with initial value or perform arithmetic or logical operation on immediate data.

To access pointer, arrays and records we need indirect addressing modes, so with direct and immediate addressing modes we cannot implement these.

MDR register needed to read or written data into or onto memory location.