51 MCU frequency division, machine cycle, clock cycle, state cycle

(2) State cycle: Each state cycle is twice the clock cycle, which is obtained by dividing the oscillation cycle by two. Detailed explanation: In the 8051 microcontroller, one clock cycle is defined as one beat (indicated by P), and two beats are defined as one state cycle (indicated by S).

(3) Machine cycle: A machine cycle consists of 6 state cycles S1~S6, that is, 12 clock cycles. In one machine cycle, the CPU can complete an independent operation.

Machine cycle

In computers, for ease of management, the execution process of an instruction is often divided into several stages, each of which completes a task. For example, fetching instructions, reading memory, writing memory, etc., each of these tasks is called a basic operation. The time required to complete a basic operation is called a machine cycle. In general, a machine cycle consists of several S cycles (state cycles). A machine cycle of the 8051 series microcontroller consists of 6 S cycles (state cycles). As mentioned earlier, a clock cycle is defined as a beat (represented by P), and two beats are defined as a state cycle (represented by S). The machine cycle of the 8051 microcontroller consists of 6 state cycles, that is, one machine cycle = 6 state cycles = 12 clock cycles

(4) Instruction cycle: It refers to the total time required for the CPU to complete an operation. Each instruction execution time consists of one or more machine cycles. In the MCS-51 system, there are single-cycle instructions, two-cycle instructions, and four-cycle instructions.

(5) Frequency division or not: When the timer/counter works in timing mode, T0x12 and T1x12 in the special function register AUXR respectively determine whether the system clock/12 (12 frequency division) or the system clock/1 (no frequency division) is used to make T0 and T1 count. When the timer/counter works in counting mode, the external pulse count is not divided. [STC12C2052AD]

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12m crystal oscillator, clock period 1/12us