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.
- 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