Data Transfer and Manipulation

Computer Organization & Embedded System — Control and Central Processing Units, NEC licence examination syllabus (Nepal Engineering Council).

Data Transfer and Manipulation: the two families of instructions

Moving data around vs actually changing it.

Every instruction set can be split into instructions that just move data (nothing computed, just relocated) and instructions that manipulate data (something is actually computed or transformed).

Transfer instructions never change the value of the data — a MOV from R1 to R2 leaves the actual bits untouched, just copies them somewhere else.

📮 Transfer Instructions

LOAD / STOREMove data between register and memory.

MOVE / EXCHANGECopy, or swap two locations.

PUSH / POPStack operations.

IN / OUTTalk to I/O ports.

🔧 Manipulation Instructions

ArithmeticADD, SUB, MUL, DIV, INC, DEC.

Logical/bitAND, OR, XOR, NOT, CLEAR, SET.

Logical shiftFills with 0.

Arithmetic shiftPreserves the sign bit — used for fast multiply/divide by powers of 2.

RotateBits that fall off one end wrap around to the other, optionally through the carry flag.

💡 A classic short-answer: "differentiate logical shift from arithmetic shift with an example." Also memorize that arithmetic left-shift by n = multiply by 2ⁿ, and arithmetic right-shift by n = divide by 2ⁿ (for signed numbers).

Syllabus points

Data transfer instructions (load, store, move, exchange, push, pop, in, out)
Data manipulation: arithmetic, logical/bit, shift (logical/arithmetic/rotate)

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