Basic knowledge: clock cycle machine cycle bus cycle instruction cycle

Clock cycle

The clock cycle is also called the oscillation cycle, which is defined as the reciprocal of the clock pulse (it can be understood that the clock cycle is the reciprocal of the single-chip microcomputer external crystal oscillator, such as the 12 m crystal oscillator, its time cycle is 1/12
Is the most basic and minimum time unit in a computer.

Within a clock cycle, the CPU performs only one basic action. For a single-chip microcomputer, if the 1 MHz clock frequency is adopted, the clock cycle is 1 us; if the 4 MHz clock frequency is adopted, the clock cycle is 250us. Because the clock pulse is the basic working pulse of the computer, it controls the working rhythm of the Computer (so that every step of the computer is unified to its pace ). Obviously, for computers of the same model, the higher the clock frequency, the faster the computer will work. However, because different computer hardware circuits and devices are not exactly the same, the clock frequency range is not necessarily the same. What we learned
The clock range of the 8051 microcontroller is 1.2 MHz-12 MHz.

In the 8051 microcontroller, a clock cycle is defined as a cycle (expressed by P), and two beats are defined as a state cycle (represented by S ).

Machine cycle

In computers, to facilitate management, the execution process of a command is often divided into several stages, each of which completes a task. For example, taking commands, reading memory, writing memory, and so on, each task is called a basic operation. The time required to complete a basic operation is called the machine cycle. Generally, a machine cycle consists of several s cycles (State cycles. 8051 series single-chip microcomputer has the same machine cycle as 6
S cycle (state cycle. As mentioned above, a clock cycle is defined as a cycle (expressed by P), and two beats are defined as a state cycle (expressed by s). The machine cycle of 8051 single-chip microcomputer is changed from 6
State cycle, that is, one machine cycle = 6 State cycles = 12 clock cycles.
Machine cycle: Generally, the minimum time for reading a script in the memory is used to specify the CPU cycle (that is
The time required for a computer to transmit information through an internal or external bus to complete one or more microoperations

Instruction cycle

A command cycle is the time required to execute a command. It generally consists of several machine cycles. The number of machine cycles varies depending on different commands. For some simple single-byte commands, after the commands are obtained into the instruction register during the instruction fetch cycle, the commands are decoded and executed immediately, and other machine cycles are no longer required. For some complex commands, such as transfer and multiplication commands, two or more machine cycles are required.

Commands that contain one machine cycle are generally called single-cycle commands. commands that contain two machines are called dual-cycle commands.

Bus Cycle

1. the microprocessor works according to the cycle under the control of the clock signal CLK. The clock frequency of the 8086/8088 system is 4.77 MHz, and each clock cycle is about ns.

2. Because the memory and I/O ports are attached to the bus, the CPU accesses the memory and I/O interfaces through the bus. Generally, the CPU is used
The time required for one access is called a bus cycle. A bus cycle generally contains four clock cycles. These four clock cycles are called four states: T1, T2, T3, and T4.

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To sum up, the relationship between them is that the command cycle is composed of several machine cycles, and the bus cycle is generally composed of four clock cycles.

Machine cycle and bus cycle ...... The machine cycle refers to the time when a basic operation is completed. This basic operation may sometimes contain bus reads and writes, and thus the bus cycle, but sometimes it may not be related to bus reads and writes, there is no explicit relationship between each other.

Command cycle: a key indicator of the CPU. It refers to the time when a command is taken and executed. Generally, a single command execution cycle and dual-command execution cycle are measured in the unit of machine cycle. Most of the current processor's commands (arm and DSP) use a single instruction execution cycle.

Machine cycle: the time unit for completing a basic operation, such as the period of the specified period and the period of the number.

Clock cycle: the reciprocal of the operating frequency of the CPU crystal oscillator. (Fantaxy: time required for a crystal oscillator)

Example: 22.1184mhz crystal oscillator, what is its crystal cycle, clock cycle, and machine cycle?

Taking 51 as an example, the crystal oscillator is 22.1184 m, and the clock cycle (crystal oscillator cycle) is (1/22. 1184) μs. One machine cycle contains 12 clock cycles, and one machine cycle is
0.5425 μs. A machine cycle generally refers to the time spent by one command, and some are instructions of two machine cycles. djnz is a dual-cycle instruction.

Fantaxy:

Cycle: the time when the task is completed.
Clock cycle: the English clock cycle; clock
Period; the clock is used for timing and is a basic unit. In the computer, the time of the CPU crystal oscillator is the most basic unit. Therefore, the clock cycle is very basic and other cycles are used for reference!