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Fetch Decode Execute is the process that a microprocessor goes through when given an instruction. This particular example is for the Intel 8080 with support chips 8228 and 8224.

Fetch (consisting of 3 parts) - Address: The Program Counter (PC) copies its contents to the Incrementer Decrementer Address Latch (IDAL). The IDAL then increments the PC and latches the address to the Address Bus

Control: The 8080 generates a MEMR (active low) (Memory Read) by simultaneously sending a STSWD (Status Word) to the 8228 and a SYNC signal to the 8224 which then sends a STSTB (active low) (Status Strobe) to the 8228 telling it that the STSWD is a control signal.

Data: The addressed location places its contents on the Data Bus

Decode - The information on the Data Bus is latched into the Information register which drives the Instruction decoder (an 8 to 256 decoder). The result of this decoding process is an active command signal which initiates the excecution of a micro program in Timing and Control.

Execute - Timing and Control runs the selected microprogram but sending out the appropriate control signals at the appropriate times.

This process is cycled through everytime an instruction is passed to the microprocessor. This is done very quickly, for example the 8080 does this in 2000 nano seconds.

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