
Internal Oscillator Characteristics
MC68HC908KX8 MC68HC908KX2 MC68HC08KX8 Data Sheet, Rev. 2.1
Freescale Semiconductor
187
17.7 Internal Oscillator Characteristics
17.8 External Oscillator Characteristics
Characteristic(1)
1. VDD = 5.5 Vdc to 2.7 Vdc, VSS = 0 Vdc, TA = –40°C to +125°C, unless otherwise noted
Symbol
Min
Typ
Max
Unit
Internal oscillator base frequency(2), (3)
2. Internal oscillator is selectable through software for a maximum frequency. Actual frequency will be
multiplier (N) x base frequency.
3.
fBus = (fINTOSC / 4) x N when internal clock source selected
fINTOSC
230.4
307.2
384
kHz
Internal oscillator tolerance
fOSC_TOL
–25
—
+25
%
Internal oscillator multiplier(4)
4. Multiplier must be chosen to limit the maximum bus frequency of 4 MHz for 2.7-V operation and 8 MHz for 4.5-V operation.
N1
—
127
—
Characteristic(1)
1. VDD = 5.5 to 2.7 Vdc, VSS = 0 Vdc, TA = –40°C to +125°C, unless otherwise noted
Symbol
Min
Typ
Max
Unit
External clock option(2), (3)
With ICG clock disabled
With ICG clock enabled
EXTSLOW = 1(4)
EXTSLOW = 0(4)
2. Setting EXTCLKEN configuration option enables OSC1 pin for external clock square-wave input.
3. No more than 10% duty cycle deviation from 50%
4. EXTSLOW configuration option configures external oscillator for a slow speed crystal and sets the clock monitor circuits
of the ICG module to expect an external clock frequency that is higher/lower than the internal oscillator base frequency,
fINTOSC.
fEXTOSC
dc(5)
60
307.2 k
5. Some modules may require a minimum frequency greater than dc for proper operation. See appropriate table for this
information.
—
32 M(6)
307.2 k
32 M(6)
6. MCU speed derates from 32 MHz at VDD = 4.5 Vdc to 16 MHz at VDD = 2.7 Vdc.
Hz
External crystal options(7), (8)
EXTSLOW = 1(4)
EXTSLOW = 0(4)
7. Setting EXTCLKEN and EXTXTALEN configuration options enables OSC1 and OSC2 pins for external crystal option.
8.
fBus = (fEXTOSC / 4) when external clock source is selected.
fEXTOSC
30 k
1 M
—
100 k
8 M
Hz
Crystal load capacitance(9)
CL
———
pF
Crystal fixed capacitance(9)
C1
—
2 x CL
—pF
Crystal tuning capacitance(9)
C2
—
2 x CL
—pF
Feedback bias resistor(9)
RB
—10—
M
10. Not required for high-frequency crystals
RS
———
M