Instruction cycle & machine cycle
- 1. INSTRUCTION CYCLE, MACHINE CYCLE & T-STATES by Manish Tadhiyal
- 2. Contents • T-states • Machine cycle • Instruction cycles • Examples • Frequency
- 3. T-States One clock period is called a T-state. One T-state Clock signals Time period of clock
- 4. Machine Cycle Machine cycle can be define as time required by the microprocessor to complete an operation of accessing memory or input / output devices. A machine cycle is comprise of some member of T-states.
- 5. There are following 5 types of machine cycle which the microprocessor can undergo: 1. OP code fetch cycle (4T-states) 2. Memory read cycle (3T-states) 3. Memory write cycle (3T-states) 4. Input / Output read cycle (3T-states) 5. Input / Output write cycle (3T-states)
- 6. Instruction cycle An instruction cycle can be define as total time required by the microprocessor to completely fetch and execute an instruction. An instruction cycle is comprised of one or more number of machine cycles.
- 7. Examples:- Lets take two different examples:- • MOV A,B here the move (MOV) command take the one machine cycle which fetch only the Op-code with 4T-states. • MVI A,35H here the move (MVI) command take the one machine cycle and initializing A with 35H takes which fetch one machine cycle i.e. Op-code+ memory read= 4T + 3T = 7T-states.
- 8. Frequency Here frequency(clock frequency) is help us to determine the time taken by the microprocessor. Usually 8085having the maximum frequency of 5MHz. By the using of the frequency we can able to find out the time period of instruction cycle.
- 9. Example Lets take the above example of MVI A,35H T=1/f =1/(5*10^6) T=0.2µs Therefore I.C= 7*0.2 = 1.4µs