MC908QY8CDWE Datasheet, PDF (217/232 Pages) Freescale Semiconductor, Inc – Addendum to MC68HC908QB8, rev. 3

Oscillator Characteristics
18.11 Oscillator Characteristics
Characteristic
Internal oscillator frequency⁽¹⁾
ICFS1:ICFS0 = 00
ICFS1:ICFS0 = 01
ICFS1:ICFS0 = 10 (not allowed if V_DD <2.7V)
Trim accuracy⁽²⁾⁽³⁾
Deviation from trimmed Internal oscillator⁽³⁾⁽⁴⁾
4, 8, 12.8MHz, V_DD ± 10%, 0 to 70°C
4, 8, 12.8MHz, V_DD ± 10%, –40 to 125°C
External RC oscillator frequency, RCCLK ⁽¹⁾⁽³⁾
External clock reference frequencyy^(1)(5)(6)
V_DD ≥ 4.5V
V_DD < 4.5V
RC oscillator external resistor⁽³⁾
V_DD = 5 V
V_DD = 3 V
Symbol
f_INTCLK
Δ_{TRIM_ACC}
Δ_{INT_TRIM}
f_RCCLK
f_OSCXCLK
R_EXT
Min
Typ
Max
—
4
—
—
8
—
—
12.8
—
—
± 0.4
—
—
±2
—
—
—
±5
2
—
10
dc
—
32
dc
16
See Figure 18-7
See Figure 18-8
Unit
MHz
%
%
MHz
MHz
—
Crystal frequency, XTALCLK^(1)(7)(8)
ECFS1:ECFS0 = 00 ( V_DD ≥ 4.5 V)
ECFS1:ECFS0 = 00
ECFS1:ECFS0 = 01
ECFS1:ECFS0 = 10
ECFS1:ECFS0 = 00 ⁽⁹⁾
Feedback bias resistor
Crystal load capacitance⁽¹⁰⁾
Crystal capacitors⁽¹⁰⁾
ECFS1:ECFS0 = 01⁽⁹⁾
Crystal series damping resistor
f_OSCXCLK = 1 MHz
f_OSCXCLK = 4 MHz
f_OSCXCLK = 8 MHz
Feedback bias resistor
Crystal load capacitance⁽¹⁰⁾
Crystal capacitors⁽¹⁰⁾
AWU module internal RC oscillator frequency
f_OSCXCLK
R_B
C_L
C₁,C₂
R_S
R_B
C_L
C₁,C₂
f_INTRC
8
8
—
32
16
1
8
30
100
—
1
—
—
20
—
—
(2 x C_L) – 5pF
—
—
20
—
—
10
—
—
0
—
—
5
—
—
18
—
—
(2 x C_L) –10 pF
—
—
32
—
MHz
MHz
MHz
kHz
MΩ
pF
pF
kΩ
kΩ
kΩ
MΩ
pF
pF
kHz
1. Bus frequency, f_OP, is oscillator frequency divided by 4.
2. Factory trimmed to provided 12.8MHz accuracy requirement (± 5%, @25•C) for forced monitor mode communication. User
should trim in-circuit to obtain the most accurate internal oscillator frequency for his application.
3. Values are based on characterization results, not tested in production.
4. Deviation values assumes trimming in target application @25•C and midpoint of voltage range, for example 5.0 V for 5 V
± 10% operation.
5. No more than 10% duty cycle deviation from 50%.
6. When external oscillator clock is greater than 1MHz, ECFS1:ECFS0 must be 00 or 01
7. Use fundamental mode only, do not use overtone crystals or overtone ceramic resonators
8. 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 Resis-
tance 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.
9. Do not use damping resistor when ECFS1:ECFS0 = 00 or 10
10. Consult crystal vendor data sheet.
MC68HC908QB8 Data Sheet, Rev. 3
Freescale Semiconductor
215