Timing Diagram of 8085 Instructions

Timing Diagram is a graphical representation. Timing diagram of 8085 instructions represents the execution time taken by each instruction in a graphical format. The execution time is represented in T-states.

Machine Cycle, T State and Instruction Cycle

T-State:

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.
A portion of an operation carried out in one system clock period is called as T-state.
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

Machine Cycles of 8085 Microprocessor

The time required to access the memory or input/output devices is called machine cycle.

Machine cycles of 8085:

The 8085 microprocessor has 5 basic machine cycles. They are

Opcode fetch cycle (4T)
Memory read cycle (3 T)
Memory write cycle (3 T)
I/O read cycle (3 T)
I/O write cycle (3 T)

Each instruction of the 8085 processor consists of one to five machine cycles, i.e., when the 8085 processor executes an instruction, it will execute some of the machine cycles in a specific order.

Instruction Cycle

The time required to execute an instruction is called instruction cycle.

Different Operations of 8085 With Respect to the Status of Various Signals

Machine Cycles of 8085

The time required to access the memory or input/output devices is called machine cycle.

The 8085 microprocessor has 5 basic machine cycles. They are

Opcode fetch cycle (4T)
Memory read cycle (3 T)
Memory write cycle (3 T)
I/O read cycle (3 T)
I/O write cycle (3 T)

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.

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.

Memory Write Machine Cycle of 8085

The memory write machine cycle is executed by the processor to write a data byte in 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.

I/O Read Machine Cycle of 8085

The I/O Read machine cycle is executed by the processor to Read a data byte from the I/O port or from a peripheral, which is I/O, mapped in the system.
The processor takes 3T states to execute this machine cycle.

I/O Write Machine 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.