What is the difference between the load capacitance of the crystal oscillator and the capacitance on both sides of the crystal oscillator? For example, I see that the capacitance on both sides of the 11.0592 crystal is 30pF. How is this 30pF calculated? What is the calculation formula?
Maia ポストする August 25, 2020
There is also why many crystal oscillators are 11.0592.
Lance ポストする August 25, 2020
The choice of 11.0592MHz is just to get the accurate communication baud rate, and the reliability of serial communication is high. Because it can be divided into clock frequency accurately, it is related to the common baud rate of UART (Universal Asynchronous Receiver/Transmitter). Especially the higher baud rate, no matter how special the value, these crystal oscillators are accurate and often used. Taking the 19.2K baud rate as an example, the 19.2K baud rate crystal oscillator is 11.0592=19200x(256-0FDH)x384x2 (19.2k SMOD is 1)
Ronan ポストする August 25, 2020
Quartz crystal oscillators have two resonant frequencies. One is a low-load capacitance crystal with a series-wound crystal oscillator; the other is a high-load-capacitance crystal with a parallel winch crystal. The nominal value of the crystal is tested with a "load capacitance" The condition is that when this condition is met during work, the oscillation frequency is consistent with the nominal value. This can be used to find the calculation formula of the crystal resonance. This is the meaning of the load capacitance. The matching capacitor of the crystal, only when the externally connected capacitor is a matching capacitor, the oscillation frequency can be guaranteed to be within the error range near the nominal frequency. This needs to be selected according to the data provided in the specification.
