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Instruction Types
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Data Transfer Instructions– operations that move data from one place to another– These instructions don’t actually modify the data, they just copy it
to the destination
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Data Operation Instructions– Unlike the data transfer instructions, the data operation instructions
do modify their data values
- They typically perform some operation using one or two data
values (operands) and store the result
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Program Control Instructions– Jump or branch instructions used to go in another part of the
program; the jumps can be absolute (always taken) or conditional(taken only if some condition is met)
- Specific instructions that can generate interrupts (software
interrupts)
Instruction formats
- An instruction is represented as a binary value with
specific format, called the
instruction code
- It is made out of different groups of bits, with
different significations:–
Opcode
- represents the operation to be performed (it is
the instruction identifier)
Operands
- one, two represent the operands of the
operation to be performed
- A microprocessor can have one format for all the
instructions or can have several different formats
- An instruction is represented by a single instruction
code
Register Addressing
- It transfers a copy of a byte or word from the source
register to the destination register.
• MOV AX,BX• MOV DX,AX
Immediate Addressing
- It transfers a source immediate byte or word of data
in to the destination register.
Register Indirect Addressing
- Transfers a byte or word between a register & a
memory location addressed by an index or baseregister.
• MOV [AX],BX• MOV [AH],BL
Base-Plus-Index Addressing
- Transfers a byte or word between a register and a
memory location addressed by a base register plusan index register.
• MOV [AX + DI],BX• MOV [DX + SI],CX
Base Relative-Plus-Index Addressing
- Transfers a byte or word between a register and a
memory location addressed by a base and an indexregister plus a displacement.
• MOV ARRAY[BX+SI],DX• MOV CX,ARRAY2[AX+DI]
ADD Instruction
- We have three forms of addition
• ADD
Addition
• ADC
Addition with Carry
• INC
Increment
• ADD AL,BL• ADD CX,DI• ADD EBP,EAX• ADD CL,44H• ADD [BX],AL• ADD CL,TEMP
ADD Instruction
• INC
- This instruction add a 1 to a register or a memory
location except segment register.
• INC BL• INC AX• INC SP• INC EAX• INC TEMP
SUB Instruction
- We have three forms of subtrtaction
• SUB
Subtraction
• DEC
Decrement
• SBB
Subtract with Borrow
• SUB CL,BL• SUB AX,SP• SUB DH,6FH• SUB [DI],CH
SUB Instruction
• DEC
- This instruction subtract a 1 from a register or a
memory location except segment register.
• DEC BH• DEC CX• DEC EDX• DEC TEMP
