What is Quartz Xtal Function?

Whether it is a passive or active quartz xtal, the quartz xtal function is to provide a clock signal source for the clock chip. 

So why does a chip need a clock signal?

For example, at urban intersections, we need traffic lights to direct traffic. What will happen if the traffic lights fail at a crowded intersection? It goes without saying that the traffic is paralyzed.

Similarly, the quartz xtal function is to provide timing guidance for all instruction programs of the chip. When the electronic digital device realizes any function, such as Bluetooth pairing connection, WiFi wireless data transmission, GPS positioning, audio, and video data processing, face recognition, or two-dimensional code scanning, the CPU has to carry out a lot of data operations, and the realization of each complex instruction involves the successful completion of the clock cycle, machine cycle, and instruction cycle.

Clock Cycle

It refers to the oscillation period or crystal period, which refers to the number of pulses per unit of time. For example, the clock cycle of a 12 MHz quartz xtal is 1 / F = 1 / 12 MHz, that is 1 / 12 microseconds. The clock cycle is the most basic and minimum time unit in a computer. In 51 MCU, a clock cycle is defined as a beat (P), and two beats are defined as a state cycle (s).

Machine Cycle

In the computer, in order to facilitate the management, the execution process of instruction is often divided into several stages, and each stage completes a task, such as fetching an instruction, reading memory, writing memory, etc.. Each of these tasks is called a basic operation. The time required to complete a basic operation is called the machine cycle. In the standard 51 single chip microcomputer, generally, a machine cycle is equal to 12 clock cycles, that is, machine cycle = 12 * clock cycles, If it is 12Mhz, then the machine cycle is 1 microsecond. When MCU works, it extracts instructions from ROM one by one and then executes them step by step. The time when a single chip computer accesses the memory is called a machine cycle, which is a time benchmark. 

Machine cycle not only plays an important role in the execution of instructions but also is the time benchmark of timer and counter of single chip microcomputer. For example, if a single-chip microcomputer chooses a 12Mhz quartz xtal, then when the value of the timer increases by 1, the actual time is 1US, which is the timing principle of a single-chip microcomputer.

Instruction Cycle

The instruction cycle 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 extraction cycle, the instructions are decoded and executed immediately after they are extracted into 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 needed.

It can be seen from the above that if the quartz xtal function is unstable or invalid, the CPU will not work normally, and eventually, the function of digital products will not be realized. We call it "broken". ”A small leak will sink a great ship” is the most appropriate one to use here.