Using The On-Chip Oscillator With A 32.768-Khz Crystal; Using An External 32.768-Khz Clock; Using The On-Chip Oscillator With A 13.000-Mhz Crystal - Intel PXA27 Series Design Manual

3.5.1.1

Using the On-Chip Oscillator with a 32.768-KHz Crystal

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The Intel
PXA27x Processor Family Electrical, Mechanical, and Thermal Specification provide
specifications for the 32.768-KHz crystal. To use the on-chip crystal oscillator, connect the 32.768-
KHz crystal between the TXTAL_IN and TXTAL_OUT pins of the processor. The on-chip
oscillator provides the required load capacitance, so do not connect external load capacitors to the
crystal. Place the crystal as close as possible to the TXTAL_IN and TXTAL_OUT pins of the
processor to minimize PCB trace length and capacitance. Route these traces parallel to each other
on the same PCB layer. If the 32.768-KHz oscillator output are used by other components in the
system, connect these inputs to the processor CLK_TOUT output and enable it. Do not attempt to
connect an external load directly to the TXTAL_OUT pin.
3.5.1.2

Using an External 32.768-KHz Clock

When using an external clock oscillator to supply the RTC timing, power up the oscillator from the
same source that is driving the VCC_BATT supply input. Connect the oscillator output to the
TXTAL_IN pin.
Note: The oscillator-output-high-drive level must be between 80% of VCC_BATT (0.8 x VCC_BATT)
and VCC_BATT. Similarly, the oscillator-output-high-drive level must be between 80% of
VCC_BATT (0.8 x VCC_BATT) and VCC_BATT. TXTAL_OUT is left floating or driving
complimentary to TXTAL_IN.
3.5.1.3

Using the On-Chip Oscillator with a 13.000-MHz Crystal

®
The Intel
PXA27x Processor Family Electrical, Mechanical, and Thermal Specification provide
specifications for the 13.000-MHz crystal. To use the on-chip crystal oscillator, connect the
13.000-MHz crystal between the PXTAL_IN and PXTAL_OUT pins of the processor. To select the
internal oscillator, ground the CLK_REQ input. The on-chip oscillator provides the required load
capacitance, so do not connect an external load capacitors to the crystal. Place the crystal as close
as possible to the PXTAL_IN and PXTAL_OUT pins of the processor to minimize PCB trace
length and capacitance. Route these traces parallel to each other on the same PCB layer. If the
13.000-MHz oscillator output is used by other components in the system, connect these inputs to
the processor CLK_PIO output and enable it. Do not attempt to connect an external load directly to
the PXTAL_OUT pin.
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Intel PXA27x Processor Family Design Guide
PXA270 Processor Electrical, Mechanical, and Thermal Specification and Intel
PXA270 Processor Electrical, Mechanical, and Thermal Specification and Intel
Clocks and Power Interface
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