Opcode fetch machine cycle of 8085 :
- Each instruction of the processor has one byte opcode.
- The opcodes are stored in memory. So, the processor executes the opcode fetch machine cycle to fetch the opcode from memory.
- Hence, every instruction starts with opcode fetch machine cycle.
- The time taken by the processor to execute the opcode fetch cycle is 4T.
- In this time, the first, 3 T-states are used for fetching the opcode from memory and the remaining T-states are used for internal operations by the processor.
Memory Read Machine Cycle of 8085:
- The memory read machine cycle is executed by the processor to read a data byte from memory.
- The processor takes 3T states to execute this cycle.
- The instructions which have more than one byte word size will use the machine cycle after the opcode fetch machine cycle.
Fig - Timing Diagram for Opcode Fetch Machine Cycle
Fig - Timing Diagram for Memory Read Machine Cycle
TIMING DIAGRAM
