The instruction IN 84H
in the 8085 microprocessor requires 5 machine cycles to complete. This includes 1 opcode fetch cycle and 4 memory read cycles. The opcode fetch retrieves the instruction from memory, while the read cycles are used to read the data from the specified input port.
In the context of the 8085 microprocessor, the ADD instruction takes 1 machine cycle to execute, as it operates directly on the accumulator and the specified register. On the other hand, the LHLD (Load H and L Direct) instruction requires 3 machine cycles, as it involves reading data from a specified memory address into the L and H registers.
The LXI H200H is a high-performance machine designed for various applications, including industrial automation and robotics. It typically operates using a cycle-based system, where machine cycles refer to the basic operational units that the machine performs to execute tasks. Each cycle involves processing instructions, moving components, or completing specific operations, and the efficiency of these cycles directly impacts the machine's overall performance and productivity. Understanding the machine cycles is essential for optimizing operations and ensuring reliable performance.
The STA (Store Accumulator) instruction typically requires one machine cycle to execute, as it directly stores the value from the accumulator into the specified memory address. However, the total number of cycles may vary depending on the specific architecture and its memory access timing. In many systems, it could take one cycle for the instruction fetch and another for the memory write, totaling two cycles. Always refer to the specific architecture documentation for precise details.
Summary − So this instruction XCHG requires 1-Byte, 4-Machine Cycles (Opcode Fetch) and 4 T-States for execution as shown in the timing diagram.
Timing Diagram is a graphical representation. It represents the execution time taken by each instruction in a graphical format. The execution time is represented in T-states.Instruction Cycle:The time required to execute an instruction is called instruction cycle.Machine Cycle:The time required to access the memory or input/output devices is called machine cycle.T-State:The machine cycle and instruction cycle takes multiple clock periods.A portion of an operation carried out in one system clock period is called as T-state.MACHINE CYCLES OF 8085:The 8085 microprocessor has 5 (seven) basic machine cycles. They areOpcode 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.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.
The STA 4200H instruction in the 8085 requires 4 machine cycles and 13 T states to complete its fetch, processing, and execution. Cycle One: Opcode fetch, 3 T states plus one opcode process state. Cycle Two: Opcode address byte 00H fetch, 3 T states Cycle Three: Opcode address byte 42H fetch, 3 T states Cycle Four: Accumulator store, 3 T states. Each cycle will have additional T-Ready states as needed by the READY pin. 13 T states is the minimum. The LDA instruction will also require 13 T states, with the last cycle being a read cycle instead of a write cycle.
1. Fetch 2. Decode 3. Execute
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RET instruction needs 3 machine cycles. One to fetch and decode the instruction(4 T states), and two more machine cycles(i.e. 2*3=6 T states) to read two bytes from the stack(stack is exterior to microprocessor, stack is in R/W memory, so to exchange data with stack needs machine cycles). Thus, RET instruction needs total 3 machine cycles and 10 T-states.
There are no instructions in the 8085 that execute in only one clock pulse. The minimum number of clock cycles is four; three for instruction fetch and one for instruction decode/execute.
Depending on the particular microprocessor, a machine cycle is the fetch or store of one (typically, one byte) native word. In the 8085, this is a byte fetch or store, plus the overhead in decoding and processing the instruction. In this case, the first machine cycle is four clock cycles, or T states, and subsequent machine cycles are three clock cycles, although certain instruction sequences, such as DAD, require two extra clock cycles.