Clock cycle, machine cycle, and command cycle

Clock cycle:Time required by a clock pulse. In computer composition principle, T cycle or Cycle Pulse. It is the basic time unit of the CPU and other single-chip microcomputer. It can be expressedClock crystal frequency(Number of clock pulses per second)The reciprocal(That is, the number of 1 S/clock pulses, such as 1/12 MHz), the CPU completes only one basic action in a clock cycle. The clock pulse is the basic working pulse of the computer and controls the working rhythm of the computer. The higher the clock frequency, the shorter the clock cycle, and the faster the operation speed. The clock cycle is also called the cycle in the CPU description. A machine cycle is divided into several equal time periods, each segment completes only one basic operation, corresponding to a level signal width. For example: (in my personal understanding) if the operating frequency is 100 MHz, the clock cycle is 1/100 m (S) = 10 (NS), and it is interpreted as 1 S (9 Power ns of 10) the number of clock periods in is 10 to the power of 8, so the time of each clock cycle is (9 to the power of 10 ns/10 to the power of 8 NS) a clock cycle, the result is 10ns.

Bus Cycle: The CPU reads commands from the memory, accesses data to the memory, reads and writes data to the peripheral port, and executes the bus cycle. The bus cycle usually contains four T states: T1, T2, T3, t4. A t state is a clock cycle. It is the minimum time unit for the CPU to perform operations.

Machine cycle:Generally, the CPU cycle (machine week) is specified by the shortest time for reading a script from the memory.Period), that is, the time required for the CPU to complete a basic operation. Generally, a machine cycle includes 12 clock cycles. In the 8051 series single-chip microcomputer, a machine cycle consists of 6 s cycles (State cycles. One s cycle = 2 beats (P), that is, one state cycle contains 2 clock cycles, so one machine cycle of 8051 Single-Chip Microcomputer = 6 State cycles = 12 clock cycles. Also known as the CPU cycle or basic cycle, bus cycle.

Instruction cycle:The time required to execute a command,It is the whole time required from command fetch, analysis command to command execution.In the computer, the execution process of a command is often divided into several stages, each of which completes a task. Each task is called a basic operation. The time required to complete a basic operation is called a machine cycle. Therefore, a command cycle is generally composed of several machine cycles. Different commands have different machine cycles. For example, a complex command may take many machine cycles to complete, and each machine cycle is completed by multiple clock cycles.

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