8085 Timing Diagram made easy | Complete Explanation with Examples

Machine Cycle Time taken by the microprocessor to perform single operation is a machine cycle. Each machine cycle is divided into T-states (Clock cycles). Time taken to perform on instruction is an instruction cycle, consisting of one or more machine cycle. Number of T-states makes a machine cycle and a machine cycles makes an instruction cycle. Machine cycles of 8085 1. Opcode fetch 2. Memory read 3. Memory write 4. I/O read 5. I/O write 6. Interrupt acknowledgment 7. Halt 8. Hold 9. Reset Instruction cycle Time taken by the processor to complete one instruction. Consists of one or more than one machine cycle. Every instruction has two parts: opcode and operand. Instructions are 1 byte, 2 byte and 3 byte long in 8085. First machine cycle of every instruction cycle is always opcode fetch i.e. reading op-code. Timing diagram Graphical representation of execution time taken by the processor for any instruction. Represents specific instruction cycle in term of machine cycles and T-states. 1 T-state represents the operation carried out in one clock period. 1- Timing diagram are graphical representation of the timing details of a processor. 2- Each instruction consists of one or more machine cycles, each machine cycle requires more than one T-state to perform the task. 3- First machine cycle of any instruction cycle is opcode fetch. 4- Timing diagram contains the status of address lines, data lines, control and status signals like RD’. WR’, IO/M’, S0. S1, ALE. 5- ALE goes high for the first clock cycle of every machine cycle. 6- When ALE goes high, AD0-AD7 contains address otherwise data.