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MC68HC908QL4 Datasheet, PDF (211/226 Pages) Motorola, Inc – Microcontrollers
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Oscillator Characteristics
Characteristic
External RC oscillator frequency, RCCLK (1)(2)
VDD ≥ 3.0 V
VDD < 3.0 V
External clock reference frequencyy(1)(4)(5)
VDD ≥ 4.5V
VDD ≥ 3.0V
VDD < 3.0V
RC oscillator external resistor
VDD = 5 V
VDD = 3 V
Crystal frequency, XTALCLK(1)(6)(7)
ECFS1:ECFS0 = 00 ( VDD ≥ 4.5 V)
ECFS1:ECFS0 = 00 (not allowed if VDD < 3.0V)
ECFS1:ECFS0 = 01
ECFS1:ECFS0 = 10
ECFS1:ECFS0 = 00 (8)
Feedback bias resistor
Crystal load capacitance(9)
Crystal capacitors(9)
ECFS1:ECFS0 = 01(8)
Crystal series damping resistor
fOSCXCLK = 1 MHz
fOSCXCLK = 4 MHz
fOSCXCLK = 8 MHz
Feedback bias resistor
Crystal load capacitance(9)
Crystal capacitors(9)
AWU Module: Internal RC oscillator frequency
Symbol
fRCCLK
fOSCXCLK
REXT
fOSCXCLK
RB
CL
C1,C2
RS
RB
CL
C1,C2
fINTRC
Min
Typ
Max
2
—
10
2
—
8.4
dc
dc
dc
—
—
—
32
16
8.4
See Figure 17-7
See Figure 17-8
8
—
32
8
—
16
1
—
8
30
—
100
—
1
—
—
20
—
—
(2 x CL) – 5pF
—
—
20
—
—
10
—
—
0
—
—
5
—
—
18
—
—
(2 x CL) –10 pF
—
—
32
—
Unit
MHz
MHz
—
MHz
MHz
MHz
kHz
MΩ
pF
pF
kΩ
kΩ
kΩ
MΩ
pF
pF
kHz
1. Bus frequency, fOP, is oscillator frequency divided by 4.
2. Deviation values assumes trimming @25°C and midpoint of voltage range, for example 5.0 V for 5 V ± 10%,
3.3 V for 3.3 V ± 10%.
3. Values are based on characterization results, not tested in production.
4. No more than 10% duty cycle deviation from 50%.
5. When external oscillator clock is greater than 1MHz, ECFS1:ECFS0 must be 00 or 01
6. Use fundamental mode only, do not use overtone crystals or overtone ceramic resonators
7. Due to variations in electrical properties of external components such as, ESR and Load Capacitance, operation above
16 MHz is not guaranteed for all crystals or ceramic resonators. Operation above 16 MHz requires that a Negative
Resistance Margin (NRM) characterization and component optimization be performed by the crystal or ceramic resonator
vendor for every different type of crystal or ceramic resonator which will be used. This characterization and optimization
must be performed at the extremes of voltage and temperature which will be applied to the microcontroller in the
application. The NRM must meet or exceed 10x the maximum ESR of the crystal or ceramic resonator for acceptable
performance.
8. Do not use damping resistor when ECFS1:ECFS0 = 00, 10 or 11
9. Consult crystal vendor data sheet.
MC68HC908QL4 Data Sheet, Rev. 7
Freescale Semiconductor
211
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