Steps involved in a Fetch Cycle - 8085

Briefly explain the steps involved in a Fetch Cycle.

Fetch cycle is the time required to fetch an opcode from a particular location in memory.

- General Fetch Cycles consist of 3T states.

- The first T state involves the sending of the memory address stored in the Program Counter to the memory.

- During the second T state the contents of the addressed memory is read ( this generally is the opcode at the specified location)

- In the third T state the opcode is sent to the Instruction register through the data bus for execution.

- For slower memories the processors has the provision to get in to the WAIT cycles as well.
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  • RE: Steps involved in a Fetch Cycle - 8085 -Akshay (08/10/15)
  • I am confused as I don't understand why would decoding require a separate cycle T4, as a decoder is a combinational circuit.
  • RE: Steps involved in a Fetch Cycle - 8085 -Rohan (06/30/15)
  • there are 4-Tstates required, as Fetch as a machine cycle means, opcode being brought up from the memory to the processor that requires 3 T-state and 1-tstate for decoding it... Fetch as a machine cycle = Opcode being brought to Instruction register + Decoding It