Datasheet

10
7764A–8051–11/07
1.3 Oscillator circuit
The on-chip oscillator is composed of a single-stage inverter and a parallel feedback resistor.
The XTAL1 and XTAL2 pins are respectively the input and the output of the inverter, which can
be configured with off-chip components as a Pierce oscillator.
Figure 1-5. Oscillator Schematic
CL: load capacitance given by crystal’s manufacturer
CI: internal capacitance of the MCU (given by the product datasheet)
CS: Stray capacitance of the circuit board
C1, C2: external capacitors
We have the following equation: CL = (C1xC2)/(C1+C2)+CI+CS
If C1=C2=CF and CS is negligible then CL = CF/2+CI and CF=2x(CL-CI)
Feedback
Resistor
XTAL1
XTAL2
GND GND
Microcontroller
C1 C2
To internal
clock circuitry
Crystal