PC Interpretation 12: Relationship between Timing Control and crystal oscillator and command cycle

The Analysis of CPU commands is to send control signals in a certain time series. In fact, all electronic devices on the bus work in the designed time series, this requires a stable and high-precision clock signal source in the computer. As early as in the IBM-PC machine, the crystal oscillator is used to provide a stable clock pulse, and the time pulse is provided to the RTC component to calculate the time, even if the PC is powered off, a button battery can be used to drive power supply to save the system time.

Frequency Doubling Technology and frequency
Later, as the CPU speed grew higher and higher, it exceeded the maximum frequency of the crystal oscillator, so it invented the Frequency Doubling technology, which amplified the crystal oscillator frequency by some means and provided the enlarged frequency to the CPU, to support the fast timing requirements of CPU. The system can use a crystal oscillator element to zoom in or out to different operating frequencies through different devices to provide different electronic devices to PCs.

The clock pulse frequency provided to the CPU becomes the CPU clock speed. The interval between two consecutive time pulses received by the CPU is called a clock cycle. The clock cycle is the smallest time unit in the computer. Within a clock cycle, the CPU performs only one basic action.

Time series control
When we analyze the time series of the value process, we find that the simplest value process requires a lot of time series work to be queued. For example, we must first control the value transmitted from the PC to Mar, then, the data in Mar is sent to the address line, and then the reading signal is sent to the bus, then the data is read from the bus to the MCM, and then the data is transmitted from the MCM to the IR, these controls must be completed successively under the time sequence control, and each step must take up a time cycle, which is only the initial part of the instruction execution process.

Instruction 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. A machine cycle consists of several clock cycles. At the same time, the time used for an access memory or I/O port operation is called a bus cycle.

Each time the CPU extracts a command and executes this command, it must complete a series of operations. The time required for such operations is usually called a command cycle. In other words, the instruction cycle is the time when an instruction is taken and executed. Different commands have different operation functions. For example, the command cycles of an addition command are different for the same multiplication command. The command cycle is often expressed by the number of machine cycles, also known as the CPU cycle. The number of machine cycles varies depending on different commands. For some simple single-byte commands, after the instruction is obtained into the instruction register in the instruction fetch cycle, the instruction is decoded immediately and no other machine cycle is 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.

Crystal Clock Source
The crystal oscillator is called a crystal oscillator. Its function is to generate the original clock frequency. After the frequency oscillator is amplified or reduced by the frequency generator, it becomes a variety of bus frequencies in the computer.

The crystal oscillator is generally called a crystal resonator. It is an electromechanical device. It is a Z crystal with a low power loss. It is made by precision cutting and grinding and plated with electrodes and welding leads.

A crystal has a very important feature. If it is powered on, it will produce mechanical oscillation. On the contrary, if it is powered on, it will generate electricity. This feature is called Mechanical and Electrical effect. They have a very important feature, and their oscillation frequency is closely related to their shape, material, and cutting direction.

Because the chemical properties of Z crystals are very stable and the thermal expansion coefficient is very small, the oscillation frequency is also very stable. Because the controlled geometric size can be very precise, the resonance frequency is also very accurate. According to the mechanical and electrical effects of Z crystal, we can regard it as an electromagnetic oscillation loop, that is, a resonant loop. Their mechanical and electrical effects are the constant conversion of machine-electricity-machine-electricity. The resonant circuit consisting of inductance and capacitance is the constant conversion of the electric field-magnetic field. The application in the circuit actually regards it as an electromagnetic resonance loop with a high Q. Because the loss of the Z crystal is very small, that is, the Q value is very high. When the oscillator is used, a very stable oscillation can be generated and used as a filter to obtain a very stable and steep band-pass or band-resistance curve.

Crystal Oscillator uses a crystal that converts electrical energy and mechanical energy to work in a resonant state to provide stable and accurate single-frequency oscillation. Under normal working conditions, the absolute accuracy of the ordinary crystal oscillator frequency can reach 50 points per million. Advanced Precision is higher. Some crystal oscillator can also adjust the frequency from the external voltage within a certain range, called a voltage controlled oscillator (VCO ).

Crystal oscillator is used to provide basic clock signals for the system. A system usually shares a crystal oscillator to facilitate synchronization of all parts. In some communication systems, the fundamental frequency and RF frequency are different crystal oscillator, while the electronic frequency adjustment method is used for synchronization.

The crystal oscillator is usually used in combination with the Phase-Locked Loop Circuit to provide the clock frequency required by the system. If different subsystems require clock signals of different frequencies, different Phase-Locked Loops connected to the same crystal oscillator can be provided.