Intel PXA26X User Manual
Page 108
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Intel® PXA26x Processor Family Developer’s Manual
Clocks and Power Manager
A 3.6864-MHz crystal must be connected between the PXTAL and PEXTAL pins. A 32.768-KHz
crystal is normally connected between the TXTAL and TEXTAL pins. This configuration gives the
lowest overall power consumption because the crystal’s resonant nature provides better power
efficiency than an external source that drives the crystal pins. Some applications have other clock
sources of the same frequency and can reduce overall cost by driving the crystal pins externally.
Refer to the Oscillator Electrical Specifications in the Intel® PXA26x Processor Family Design
Guide for more information.
Note:
No external capacitors are required.
3.8.3
Noise Coupling Between Driven Crystal Pins and a Crystal
Oscillator
The two pairs of crystal pins are located near each other on the processor. When crystal oscillators
are connected to the pins, this proximity leads to low-signal swings and slow edges that result in
limited-noise coupling between the pins. If one of the crystal oscillators is replaced by an
independent-signal source and the other is not, the noise coupling may increase. To limit this effect,
reduce the slew rate on the pins driven by the independent source.