Internal Oscillator Characteristics
MC68HC908GT16 MC68HC908GT8 MC68HC08GT16 Data Sheet, Rev. 5.0
Freescale Semiconductor
261
20.10 Internal Oscillator Characteristics
20.11 External Oscillator Characteristics
Characteristic
(1)
1. V
DD
= 5.5 Vdc to 2.7 Vdc, V
SS
= 0 Vdc, T
A
= T
A
(min) to T
A
(max), unless otherwise noted
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
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.
Symbol
Min
Typ
Max
Unit
Internal oscillator base frequency
(2), (3)
f
INTOSC
230.4
307.2
384
kHz
Internal oscillator tolerance
f
OSC_TOL
–25
—
+25
%
Internal oscillator multiplier
(4)
N
1
—
127
—
Characteristic
(1)
1. V
DD
= 5.5 to 2.7 Vdc, V
SS
= 0 Vdc, T
A
= T
A
(min) to T
A
(max), unless otherwise noted
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.
5. Some modules may require a minimum frequency greater than dc for proper operation. See appropriate table for this
information.
6. MCU speed derates from 32 MHz at V
DD
= 4.5 Vdc to 16 MHz at V
DD
= 2.7 Vdc.
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.
9. Consult crystal vendor data sheet, see
Figure 7-4. External Clock Generator Block Diagram
.
10. Not required for high-frequency crystals
Symbol
Min
Typ
Max
Unit
External clock option
(2)(3)
With ICG clock disabled
With ICG clock enabled
EXTSLOW = 1
(4)
EXTSLOW = 0
(4)
f
EXTOSC
dc
(5)
60
307.2 k
—
—
—
32 M
(6)
307.2 k
32 M
(6)
Hz
External crystal options
(7)(8)
EXTSLOW = 1
(4)
EXTSLOW = 0
(4)
f
EXTOSC
30 k
1 M
—
—
100 k
10 M
Hz
Crystal load capacitance
(9)
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
—
M
Ω
Series resistor
(9)(10)
R
S
—
—
—
M
Ω