Timing Diagram.pptx
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The document explains the concepts of instruction cycle, machine cycle, and t-states in the context of the 8085 microprocessor, detailing how instructions are fetched, decoded, and executed over different cycles. An instruction cycle is the time taken to complete an instruction, consisting of fetch and execute cycles, while machine cycles refer to the read/write operations involved, determined by the specific instruction being executed. T-states, representing the time for a single clock cycle, are critical in calculating execution time for operations within the microprocessor.
Timing Diagram.pptx
- 1. Instruction cycle, Machine cycle & T-states 1
- 2. Instruction cycle • Instructions are contained in the memory and is pointed by the program counter. • It is first moved to the instruction register and is decoded in binary form and stored as an instruction in the memory. • The computer takes a certain period to complete this task i.e., instruction fetching, decoding and executing on the basis of clock speed. • Such a time period is called ‘Instruction cycle’ and consists two cycles namely Fetch cycle and Execute cycle. 2
- 3. Instruction cycle • Instruction cycle can be defined as the time taken to complete an instruction. • We can also say that an instruction cycle is defined as the sequence of operations that are required by the CPU to fetch an instruction and data from the memory and to execute it. • The instruction cycle consists of a fetch cycle and a execute cycle. • The sequence of operations which are required to fetch an opcode from the memory constitute a fetch cycle. • The necessary steps which are required to get data from the memory and to perform the operation specified by an instruction constitute an execute cycle. 3
- 4. • Instruction Cycle = Fetch Cycle + Execute Cycle • An instruction cycle consists of one to six machine cycles 4
- 5. Machine Cycle • Each READ or WRITE operations of the 8085 is referred to as Machine Cycle. • An 8085 instruction’s execution consists of a number of machine cycles. • These cycles vary from one to five (M1 to M5) depending on the instruction. • Each machine cycle contains a number of clock cycles (also referred to as T-states). 5
- 6. • The time required to complete one operation; accessing either the memory or I/O device. • A machine cycle consists of three to six T-states. 6
- 7. T-state • T-state may be defined as the time taken by the clock to complete one period. • Time corresponding to one clock period. • It is the basic unit to calculate execution of instructions or programs in a processor. • A T-state is measured from the falling edge of one clock pulse to the falling edge of the next clock pulse. • Fetch cycle takes four t-states and execution cycle takes three t-states 7
- 9. T-States, Machine and Instruction Cycle 9 Instruction Cycle Machine Cycle T-States Time required to complete execution of an instruction. Time required by the microprocessor to complete an operation. Operation performed in one clock period.
- 10. T-States • “T-States are defined as operation performed in one clock period.” • These sub-divisions are internal states synchronized with system clock & each T-state is precisely equal to one clock period. 10 CLK Clock Period
- 11. Machine Cycle • “Machine Cycle is defined as time required by the microprocessor to complete an operation.“ • This cycle may consist 3 to 6 T-states. • The basic microprocessor operation such as reading a byte from I/O port or writing a byte to memory. 11 T1 T2 T3 T4 T1 T2 T3 T1 T2 T3 Opcode Fetch Memory Read CLK I/O Write Machine Cycle-1 Machine Cycle-2 Machine Cycle-3 m/m Read
- 12. Instruction Cycle • “Instruction Cycle is defined as time required to complete execution of an instruction. “ • In 8085 microprocessor instruction cycle consists of 1 to 6 Machine Cycles or 1 to 6 operations. 12 CLK
- 14. Timing Diagram • Representation of Various Control signals generated during Execution of an Instruction. • Following Buses and Control Signals must be shown in a Timing Diagram: •Higher Order Address Bus. •Lower Address/Data bus •ALE •RD •WR •IO/M’ 14
- 15. 15 High order memory address Unspecified Low order M/m addr. Opcode CLK A8 AD0 AD7 ALE IO/M RD A15 Opcode Fetch
- 16. 16 High order memory address Low order M/m addr. Data from memory CLK A8 AD0 AD7 ALE IO/M RD A15 Memory read cycle S1 S0 Mode 0 0 HLT 0 1 WRITE 1 0 READ IO/M=0, S1=1 , S0=0 S1 S0
- 17. 17 High order memory address Low order M/m addr. Data from Microprocessor CLK A8 AD0 AD7 ALE IO/M WR A15 Memory write cycle S1 S0 Mode 0 0 HLT 0 1 WRITE 1 0 READ IO/M=0, S1=0 , S0=1 S0 S1
- 18. 18 High order I/O address Low order I/O addr. I/O data CLK A8 AD0 AD7 ALE IOR A15 I/O read cycle S1 S0 Mode 0 0 HLT 0 1 WRITE 1 0 READ IO/M=1, S1=1 , S0=0 IO/M S1 S0
- 19. 19 High order I/O address Low order I/O addr. Data from Microprocessor CLK A8 AD0 AD7 ALE IOW A15 I/O write cycle S1 S0 Mode 0 0 HLT 0 1 WRITE 1 0 READ IO/M=1, S1=0 , S0=1 IO/M S0 S1
- 20. 20 Timing Diagram : MOV B,M T1 T2 T3 T4 T5 T6 T7 CLK A8 AD0 AD7 ALE IO/M A15 High order memory address Unspe cified High order memory address Low order M/m addr. Opcode Low order M/m addr. Data from memory RD Opcode Fetch Memory Read
- 21. 21 Timing Diagram : MVI A, 32H T1 T2 T3 T4 T5 T6 T7 CLK A8 AD0 AD7 ALE IO/M A15 High order memory address Unspe cified High order memory address Low order M/m addr. Opcode Low order M/m addr. Read Immediate RD Opcode Fetch Memory Read
- 22. Calculate Execution time of MVI A,32H Given: Clock Frequency (f) = 2 MHz Calculation: Step-1: T-state = clock period = 1 𝑓 = 1 2 = 0.5 sec Step-2: Execution time for Opcode Fetch = 4T x 0.5 = 2sec Step-3: Execution time for Memory Read = 3T x 0.5 = 1.5sec Step-4: Execution time for Instruction = (4T + 3T) x 0.5 = 7T x 0.5 = 3.5sec 22
- 23. Timing Diagram : IN 02H Opcode Fetch Memory Read T1 T2 T3 T4 T1 T2 T3 T1 T2 T3 CLK A8 AD0 AD7 ALE IO/M A15 High order memory address High order memory address Unspecif ied Port address 02H RD IOR Low addr 02H Low addr Opcode Port addr Acc. content I/O Read 23
- 24. Timing Diagram : OUT 02H Opcode Fetch Memory Read T1 T2 T3 T4 T1 T2 T3 T1 T2 T3 CLK A8 AD0 AD7 ALE IO/M A15 High order memory address High order memory address Unspecif ied Port address 02H RD IOW Low addr 02H Low addr Opcode Port addr Acc. content I/O Write 24
- 25. More Notes in with explanation 25
- 26. MACHINE CYCLES OF 8085 The 8085 microprocessor has 5 basic machine cycles. They are 1. Opcode fetch cycle (4T) 2. Memory read cycle (3 T) 3. Memory write cycle (3 T) 4. I/O read cycle (3 T) 5. I/O write cycle (3 T)
- 27. MACHINE CYCLES OF 8085 • The processor takes a definite time to execute the machine cycles. The time taken by the processor to execute a machine cycle is expressed in T-states. • One T-state is equal to the time period of the internal clock signal of the processor. • The T-state starts at the falling edge of a clock.
- 28. OPCODE FETCH MACHINE CYCLE OF 8085
- 29. 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.
- 30. MEMORY READ MACHINE CYCLE OF 8085
- 31. 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.
- 32. MEMORY WRITE MACHINE CYCLE OF 8085
- 33. MEMORY WRITE MACHINE CYCLE OF 8085 • The memory write machine cycle is executed by the processor to write a data byte in a memory location. • The processor takes, 3T states to execute this machine cycle
- 34. I/O READ CYCLE OF 8085 • The I/O Read cycle is executed by the processor to read a data byte from I/O port or from the peripheral. • The processor takes 3T states to execute this machine cycle. • The IN instruction uses this machine cycle during the execution.
- 35. I/O READ CYCLE OF 8085
- 36. I/O WRITE CYCLE OF 8085 • The I/O write machine cycle is executed by the processor to write a data byte in the I/O port or to a peripheral, which is I/O, mapped in the system. • The processor takes, 3T states to execute this machine cycle.
- 37. I/O WRITE CYCLE OF 8085
- 38. EXAMPLE INSTRUCTION : MVI B, 43
- 39. EXAMPLE INSTRUCTION : STA 526A