In microcontroller technology, cycles are a very important concept. According to their types, cycles can be divided into clock cycles, machine cycles, instruction cycles, and bus cycles. Although they have different definitions and functions, they are interrelated during the operation of the microcontroller. Below we will discuss these cycles.
1. Clock Cycle
The clock cycle is the basic time unit for the operation of the microcontroller. It represents a complete cycle of the internal clock signal of the microcontroller. During each clock cycle, the microcontroller performs one basic operation or state update.
The length of the clock cycle determines the operating speed of the microcontroller; the shorter the clock cycle, the faster the microcontroller operates.
2. Machine Cycle
The machine cycle is the time required for the microcontroller to complete one basic operation, typically composed of several clock cycles. A machine cycle can complete operations such as fetching instructions, decoding, and executing.
The length of the machine cycle depends on the design of the microcontroller and the complexity of the instruction set.
3. Instruction Cycle
The instruction cycle is the time required for the microcontroller to execute an instruction. It includes multiple stages such as fetching the instruction, decoding, and executing, thus typically consisting of several machine cycles.
The length of the instruction cycle is related to the complexity of the instruction and the performance of the microcontroller. Different instructions may have different instruction cycles.
4. Bus Cycle
The bus cycle is the time required for the microcontroller to exchange data with external devices or memory. During the bus cycle, the microcontroller sends or receives data through the bus to complete communication with external devices.
The length of the bus cycle depends on the data transfer rate and the characteristics of the bus.
5. Differences
These four cycles each have their roles in the operation of the microcontroller, yet they are interrelated. The clock cycle is the most basic time unit, the machine cycle is the time for the microcontroller to complete basic operations, the instruction cycle is the time to execute an instruction, while the bus cycle is the time for communication with external devices.
The relationship among them can be expressed as follows: the instruction cycle contains several machine cycles, the machine cycle contains several clock cycles; the bus cycle is related to the data transfer rate of the microcontroller and the characteristics of the bus, and its length does not necessarily have a fixed ratio to the machine cycle or instruction cycle.
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