Oscillator Characteristics
MC68HC908QL4 MC68HC908QL3 MC68HC908QL2 Data Sheet, Rev. 4
Freescale Semiconductor
211
External RC oscillator frequency, RCCLK
(1)(2)
V
DD
≥ 3.0
V
V
DD
<
3.0 V
External clock reference frequencyy
(1)(4)(5)
V
DD
≥
4.5V
V
DD
≥
3.0V
V
DD
< 3.0
V
RC oscillator external resistor
V
DD
= 5 V
V
DD
= 3 V
Crystal frequency, XTALCLK
(1)(6)(7)
ECFS1:ECFS0
= 00 ( V
DD
≥
4.5 V)
ECFS1:ECFS0
= 00 (not allowed if V
DD
<
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
f
OSCXCLK
= 1 MHz
f
OSCXCLK
= 4 MHz
f
OSCXCLK
=
8 MHz
Feedback bias resistor
Crystal load capacitance
(9)
Crystal capacitors
(9)
f
RCCLK
2
2
—
—
10
8.4
MHz
f
OSCXCLK
dc
dc
dc
—
—
—
32
16
8.4
MHz
R
EXT
See
Figure 17-7
See
Figure 17-8
—
f
OSCXCLK
8
8
1
30
—
—
—
—
32
16
8
100
MHz
MHz
MHz
kHz
R
B
C
L
C
1
,C
2
—
—
—
1
20
(2 x C
L
) – 5pF
—
—
—
M
pF
pF
R
S
R
B
C
L
C
1
,C
2
f
INTRC
—
—
—
—
—
—
20
10
0
5
18
(2 x C
L
) –10 pF
32
—
—
—
—
—
—
k
k
k
M
pF
pF
AWU Module: Internal RC oscillator frequency
—
—
kHz
1. Bus frequency, f
OP
, 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.
Characteristic
Symbol
Min
Typ
Max
Unit