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To drive the 32.768-kHz crystal pins from an external source
•
Drive the TEXTAL pin with a digital signal that has a low level near 0 volts and a high level
near VCC. Do not exceed VCC or go below VSS by more than 100 mV. The minimum slew
rate is 1 volt per 1 µs. The maximum current sourced by the external clock source when the
clock is at its maximum positive voltage should be approximately 1 mA.
•
Float the TXTAL pin or drive it complementary to the TEXTAL pin, with the same voltage
level, slew rate, and input current restrictions.
4.6.2
3.6864 MHz Oscillator Specifications
The 3.6864-MHz oscillator is connected between the PXTAL (amplifier input) and PEXTAL
(amplified output).
Table 14. 3.6864-MHz Oscillator Specifications
Symbol
Crystal Specifications - Typical is FOX HC49S
F
XP
ESR
P
Amplifier Specifications
VIH_X
VIL_X
IIN_XP
CIN_XP
tS_XP
Board Specifications
RP_XP
CP_XP
COP_XP
To drive the 3.6864-MHz crystal pins from an external source
•
Drive the PEXTAL pin with a digital signal with a low level near 0 volts and a high level near
VCC. Do not exceed VCC or go below VSS by more than 100 mV. The minimum slew rate is
1 volt / 100 ns. The maximum current sourced by the external clock source when the clock is
at its maximum positive voltage should be approximately 1 mA.
•
Float the PXTAL pin or drive it complementary to the PXTAL pin, with the same voltage
level, slew rate, and input current restrictions. If floated, some degree of noise susceptibility
will be introduced in the system; therefore, it is not recommended.
Intel® PXA255 Processor Electrical, Mechanical, and Thermal Specification
Table 14
shows the 3.6864-MHz specifications.
Description
Crystal Frequency, PXTAL/PEXTAL
Equivalent series resistance, PXTAL/PEXTAL
Drive Level
Input High Voltage, PXTAL
Input Low Voltage, PXTAL
Input Leakage, PXTAL
Input Capacitance, PXTAL/PEXTAL
Stabilization Time
Parasitic Resistance, PXTAL/PEXTAL to any node
Parasitic Capacitance, PXTAL/PEXTAL, total
Parasitic Shunt Capacitance, PXTAL to PEXTAL
Electrical Specifications
Min
Typical
Max
—
3.6864
—
50
-
300
—
—
100
0.8*VCC
VCC
VSS
0.2*VCC
10
40
50
17.8
67.8
20
5
0.4
Units
MHz
Ω
uW
V
V
µA
pF
ms
MΩ
pF
pF
29
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