Free Electronic Circuits & 8085 projects

Electronic projects with circuit diagram and 8085 microprocessor projects.

Opcode Fetch and Memory Read Machine Cycle – Timing Diagram

Published on Jun 18 2014 // Timing Diagram

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.

Fig – Timing Diagram for Opcode Fetch Machine Cycle

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 Memory Read Machine Cycle

Timing Diagram of Machine cycles…(Contd) – >>Page3