Timing Diagram 8085 Microprocessor

A time diagram is a graphical representation where the 8085 instruction timing diagram represents the execution time of each instruction in graphical format. In this article, we will be Going Through the Timing Diagram, We will go through Different Machine Cycles Such as Opcode Fetch, Memory Read, Memory Write, I/O Read, and I/O Write, Then we will go through the Timing Diagram of Some Instructions such as MVI, STA, and INR, At last, we will conclude our Article with Applications and Some FAQs.

Table of Content

• What is a Timing Diagram?
• Machine Cycle of 8085
• Opcode fetch machine cycle of 8085
• Memory Read Machine Cycle of 8085
• Memory Write Machine Cycle of 8085
• I/O Read Machine Cycle
• I/O Write Machine Cycle
• Timing Diagram of Some Instructions

What is a Timing Diagram?

A time diagram is a graphical representation. The 8085 instruction timing diagram represents the execution time of each instruction in graphical format. Execution time is given in T-states. The 8085 microprocessor has a set of control signals and data signals that play an important role in the execution of instructions. In this article, I will explain in detail what a timing diagram is and how to draw a timing diagram of different instructions

• Clock Signal: The time required to execute an instruction is called a clock cycle.
• Machine Cycle: The time required to access memory or input/output devices is called a machine cycle. The 8085 has 5 basic machine cycles i.e., load opcode, read from memory, write to memory, read I/O, and write I/O.
• T-State: A machine cycle and an instruction cycle take several clock periods. The portion of an operation performed in one system clock period is called a T-state.
• Control Signals: The control signal controls the operations. Common signals are ALE (address block enable), RD (read), WR (write), and IO/M (input/output) memory.

Machine Cycle of 8085

The 8085 microprocessor has 5 basic machine cycles. They are :

• Opcode Fetch
• Memory Read
• Memory Write
• I/O Read
• I/O Write

Opcode Fetch Machine Cycle of 8085

• Each processor instruction has a one byte opcode.
• Operation codes are stored in memory. Thus, the processor performs an opcode load machine cycle to load the opcode from memory.
• Thus, each instruction begins with a machine cycle of opcodes.
• The time the processor takes to perform an opcode load cycle is 4T.
• At this time, the first, 3T-states are used to load the opcode from memory, and the remaining T-states are used for internal opcodes.

Opcode Fetch Cycle

Memory Read Machine Cycle of 8085

• A memory read machine cycle is executed by the processor to read a data byte from memory.
• The processor takes 3T states to perform this cycle.
• Instructions that have more than one byte word will use machine cycle after machine cycle to load the opcode.

Memory Read Machine Cycle

Memory Write Machine Cycle of 8085

• A write-to-memory machine cycle is executed by the processor to write a data byte to memory.
• The processor takes 3T states to perform this cycle.
• Instructions that have more than one byte word will use machine cycle after machine cycle to load the opcode.

Memory Write Machine Cycle

I/O Read Machine Cycle

• A reader I/O cycle is performed by the processor to read a data byte from an I/O port or peripheral that is I/O mapped in the system.
• The processor needs 3T states to execute this machine cycle.

I/O Read Machine Cycle

I/O Write Machine Cycle

• A writer’s I/O cycle is executed by the processor to write a data byte to an I/O port or peripheral that is I/O mapped in the system.
• The processor needs 3T states to execute this machine cycle.

I/O Write Machine Cycle

Timing Diagram of Some Instructions

• MVI A,45
• STA 8000H
• INR M

Timing Diagram of MVI A,45

• Loading opcode 4EH from memory 2000H. (Operation Code Loading Machine Cycle)
• Read (move) data 45H from memory 2001H. (memory reading).

Timing Diagram of MVI Instructions

Timing Diagram of STA 8000H

• STA stands for Store Accumulator – the contents of the accumulator are stored at (1000H).
• The transaction code of STA indicates 32H. It is provided by 1000H memory (see picture). – In the machine cycle.
• Then read the sub address (00). – Memory reading machine cycle
• Read higher memory location (80) – Memory read machine cycle.
• Consider the combination of the two addresses and write the details of the accumulator for 8000. – Don’t forget to write the machine cycle
• Assume the memory address for the instruction and let the content of accumulator is C7H. So, C7H from accumulator is now stored in 8000H.

Timing Diagram of STA Instructions

Timing Diagram of INR M Instructions

• C500H INR M 34H
• D050 as memory address
• E1H and E2H as opcode
  

Timing Diagram of INR Instructions

Applications 0f 8085

• System charts keep track of all changes occurring in the system.
• Timelines provide a more accurate representation of physical activity.
• The timing table of 8085 instructions graphically represents the time required to execute each instruction.
• Timing Diagram is a special form of sequence diagram.
• Timing Diagram keep track of every change that occur in the system.
• The timing diagram is important for planning the clock frequency of the microprocessor.
• The timing diagram helps design memory circuits that meet the required set and hold times during read and write operations.

Conclusion

The timing diagram of the 8085 microprocessor looks like a brief overview of how the microprocessor works during operation. It helps engineers solve problems, create good memories and interactions between devices, make quick decisions, and do good, on-time work. For students, it simplifies the learning process by providing a visual representation of the inner workings of a microprocessor. Essentially, it serves as a guide for understanding, troubleshooting and optimizing the performance of the 8085 microprocessor.

FAQs on Timing Diagram 8085 Microprocessor

What does a timing diagram show?

A sequence diagram contains time information for at least one horizontal line as well as a vertical line that transitions between states.

Why do we use timing diagram?

Timing graphs are used to understand, design, and troubleshoot timing relationships between signals in microprocessors and digital systems; thus aiding in debugging, optimization and learning.

What is another name of timing diagram

The another name of timing diagram is sequence diagram.