What is the Duty Cycle of 12MHz Crystal Oscillator?

12MHz crystal oscillator is a very common crystal oscillator frequency. The common models include passive SMD3225, active SMD3225, DIP49S, 49SMD, etc..

The main electrical parameters are as follows:

Optional Adjustment Frequency Tolerance: ± 10ppm, ± 20ppm, ± 30ppm (at 25 ℃)

Optional Temperature Frequency Stability: ± 10ppm, ± 20ppm, ± 30ppm

Optional Working Temperature (℃): - 20 ~ + 70, - 40 ~ + 85

Optional Load Capacitance: 12PF, 20pF or custom

Specifically, computers have a timing circuit. Although the term "clock" is generally used to refer to these devices, they do not actually refer to real-time clock (RTC) in the normal sense. It may be more accurate to call them timers. How many times does a 12MHz crystal oscillator vibrate in one second? The unit of frequency is Hertz, which means the number of vibrations per second. 12MHz = 12000000Hz, which means 12 million vibrations per second.

What is the machine cycle of 12Mhz crystal oscillator?

Clock period is the time period, also known as clock oscillation period = 1 / 12MHz = 0.083us

Machine cycle = 12 * clock cycle = 12 / 12MHz = 1us

So, what is the duty cycle of 12MHz crystal oscillator?

12MHz crystal oscillator, its time period is 1 / 12 us.

The duty cycle is different according to the type of single chip microcomputer and the instruction, which should be analyzed in detail.

Machine cycle

In the computer, in order to facilitate management, the execution process of an instruction is often divided into several stages, each stage completes a task. For example, fetching instructions, memory reading, memory writing, etc.. Each of these tasks 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 cycles (state cycles). One machine cycle of 8051 series single chip microcomputer is composed of six s cycles (state cycle). 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 8051 single chip microcomputer consists of 6 State cycles, that is, one machine cycle = 6 State cycles = 12 clock cycles.

Duty Cycle

It is the time required to execute an instruction, which is generally composed of several machine cycles. Different instructions require different machine cycles. For some simple single byte instructions, in the instruction fetch cycle, the instructions are decoded and executed immediately after they are fetched to the instruction register, and no other machine cycle is needed. For some complex instructions, such as transfer instruction and multiplication instruction, two or more machine cycles are required. Generally, an instruction with one machine cycle is called a single cycle instruction, and an instruction with two machine cycles is called a double cycle instruction. 

In short, without crystal oscillator, there will be no clock cycle. Without clock cycle, the program code cannot be executed, and the MCU cannot work.