Datasheet
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. V
DD
= 5.5 Vdc to 2.7 Vdc, V
SS
= 0 Vdc, T
A
= –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.
f
Bus
= (f
INTOSC
/ 4) x N when internal clock source selected
f
INTOSC
230.4 307.2 384 kHz
Internal oscillator tolerance
f
OSC_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. V
DD
= 5.5 to 2.7 Vdc, V
SS
= 0 Vdc, T
A
= –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,
f
INTOSC.
f
EXTOSC
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 V
DD
= 4.5 Vdc to 16 MHz at V
DD
= 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.
f
Bus
= (f
EXTOSC
/ 4) when external clock source is selected.
f
EXTOSC
30 k
1 M
—
—
100 k
8 M
Hz
Crystal load capacitance
(9)
9. Consult crystal vendor data sheet, see Figure 7-3. External Clock Generator Block Diagram.
C
L
———pF
Crystal fixed capacitance
(9)
C
1
—
2 x C
L
—pF
Crystal tuning capacitance
(9)
C
2
—
2 x C
L
—pF
Feedback bias resistor
(9)
R
B
—10—MΩ
Series resistor
(9), (10)
10. Not required for high-frequency crystals
R
S
———MΩ