INSTRUCTION SETT S PRADEEP KUMAR

Assistant Professor (SG)

VIT University – Chennai Campus

http://www.pradeepkumar.org

tspembedded@gmail.com

Topics to be covered• Instruction Formats• Types of Operations• Addressing Modes

Instruction Format• Elements of a machine instruction

• Operation Code – specifies the operation to be performed and this is a binary code.

• Source Operand Reference – operands that are inputs• Result Operand reference – operand that are outputs• Next instruction reference - This tells the processor where to fetch

the next instruction after the execution of this instruction is complete

Instruction Format• Operand Location

• Main or Virtual Memory• Processor Register – a processor contains one or more register. In

there is only one, reference is implicit. Else the register number is to be supplied.

• Immediate – The value of the operand is contained in a field in the instruction being executed

• I/O device - The instruction must specify the I/O module and device for the operation.

Instruction Format• A Simple Instruction Format

Instruction Format

Instruction Format

Operations• Data transfer• Arithmetic• Logical• Conversion• I/O• System control• Transfer of control

Data Transfer OperationOperation Name Description

Move (Transfer) Transfer word or block from source todestination

Store Transfer word from processor to memory

Load (fetch) Transfer word from memory to processor

Exchange Swap contents of source and destination

Clear (Reset) Transfer word of 0s to destination

Set Transfer word of 1s to destination

PUSH Transfer word from source to top of stack

POP Transfer word from top of stack todestination

Arithmetic• ADD• Subtract• Multiply• Divide• Absolute – replace operand by its absolute value• Negate – change sign of operand• Increment – add 1 to operand• Decrement – subtract 1 from operand

Logical• AND, OR, NOT, X OR• Test• Compare• Set control variables• Shift• Rotate

Transfer of Control• Jump (Branch) – load PC with specified address• Jump conditional • Jump to subroutine• Return• Execute• Skip – increment PC to next instruction• Skip conditional • Halt – stop program execution• Wait• No Operation

I/O• Input (read) -Transfer data from specified I/O port or

device to destination (e.g., main memory or processor register)

• Output (write) -Transfer data from specified source to I/O port Input/Output or device

• Start I/O -Transfer instructions to I/O processor to initiate I/O operation

• Test I/O -Transfer status information from I/O system to specified destination

Addressing modes• The manner in which target address or effective address

is identified within the instruction is called addressing mode

• Immediate Addressing• Direct Addressing• Indirect Addressing• Register Addressing• Register Indirect Addressing• Displacement Addressing• Stack Addressing

Immediate addressing

Immediate addressing• Simplest form of addressing• Operand value is present directly

• Operand = A

• Useful for defining constants or set initial values

Direct addressing

Direct addressing• EA = A• Effective address is just the address of the operand• It only provides limited address space

Indirect addressing

Indirect addressing• EA =(A) • Parentheses specifies the contents of A• Neither the address of the operand nor the operand • Disadvantage: Two memory references to fetch the

operand

Register addressing

Register addressing• EA = R• Similar to direct addressing.• Address field refers to register rather than a main memory

address• Advantages: only a small address field is needed, no time

consuming memory references• Disadvantages: only limited registers are available in any

processors when compared to main memory.

Register indirect addressing

Register indirect addressing• EA = (R)• Similar like indirect addressing, but instead of main

memory, the reference is the register.

Displacement addressing

Displacement addressing• EA = A + (R) • Combination of direct addressing and register indirect

addressing• Very effective • Operates in three modes

• Relative addressing• Index addressing• Base register addressing

Stack addressing

Stack addressing• Linear array of locations• Pushdown list or Last in First out List• Elements are appended to the top of the stack• Stack pointer is maintained in a register.• the operation performed at the top of the stack

Together

QUESTIONS???