Subject Code : Name Of Subject : Microprocessor and assembly language programming Name of Unit : Instruction cycle and Timing diagram Topic : Instruction cycle Name of Faculty : H.M.Avaiya & N.D.Dhameliya Name of Students: (i) SAINI SHIVANISINGH J(091) (ii) PANDYA DHVANIBEN D(092)

Instruction Cycle

 The microprocessor primarily performs four operations as listed below: 1.Memory read-to read data from memory 2.Memory write-to write data into memory 3.I/O read-to take data from input device 4.I/O write-to send data from output device

 Example:- Let us consider the timing and execution of MOV A, B instruction stored in the program memory. This example is for 1 bit instruction.  op code fetch Memory locationInstructionMachine code 2000hMOV A, B78h

 In this opcode fetch four T-state are used.  T-state:- each operation of the microprocessor is performed in synchronization with the internal clock. One clock pulse is called T-state.  ALE:  It stands for Address Latch Enable.  when it is high it indicates address and when it is low it indicates data and opcode.

A8-A15:  It indicates higher order address.  In this cross is indicates the muitibit line is given.  In this example higher order address is 20h. AD7-ADO:  It is the multiple line to data/add line.  so for this example ooh is the lower order address and 78h is op code. IO/M:  In op code fetch IO/M is IO/M=0 S1=1 S2=2

Example: Let us consider the timing and execution of MVI A, FFh instruction stored in program memory.  When 2 byte instruction is given draw op code fetch and memory read together. Memory locationInstructionMachine code 2000h 2001h MVI A, FFh3Eh FFh

 Memory read AND memory write:  In memory read cycle store the data from memory.  MEMR signal enable the memory device for read operation.  The memory write operation is also very similar to memory read operation except it uses WR signal to generate MEMW signal as shown in figures.

 The RD and WR signals are used with IO/M = 1 to generate IOR and IOW control signals required to complete the I/O read and I/O write operation.

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