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more values will make the oscillator more accurate, but slower start. For hi freq oscillator this is not so actual, like in clock 32768 for example.
More valure will increase the oscillator power consumption. And value greater then 30pf not recommended because the oscillator could be fail to start
The value of 30pF is not critical, in most cases anything between 15pF and 40pF should work fine ..
If you don't use serial port 12MHz is as good as 11,0952MHz, or even better, as it is easier to more accurately generate ms delays .. 12MHz:12 ..etc
If you use UART 11.0952MHz frequency helps to more accurately generate frequencies required for commonly used baud rates ..
almost all basic 8051 connection circuit have 18th and 19th pin connected to an oscillator having 11.0592 mhz and two capacitors connected to it have value 30pf.
please explain me the basic 8051 connection diagram.
To make an oscillator you need 'gain' to overcome the component losses and 'phase shift' so the feedback is in the right polarity. To achieve this inside the 8051 there is an inverter (providing the gain and some of the phase shift) wired across pins 18 and 19 inside the IC. The crystal and the two capacitors provide the remaining phase shift. The frequency is decided primarily by the crystal which will only allow feedback at one frequency (at least in this simple circuit). The capacitors load the inverter and crystal to complete the resonant circuit. The frequency will vary slightly (a few KHz at most) if the capacitor values are changed but the crystal provides almost all the frequency control.
If the capacitors are made too large the overall gain will be lower and oscillator will take longer to start up. Beyond a certain value the oscillator will not start at all.
If they are made too small, the crystal, the 8051 and the circuit board become the dominant capacitances and all of these are less predictable and more prone to changing with temperature.
The suggested values are a compromise that satisfy the fast start requirement and give good stability.
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