AN2727 Freescale Semiconductor / Motorola, AN2727 Datasheet - Page 15

• Manufacturer Part Number: AN2727
• Description: Designing Hardware for the HCS12 D-Family
• Manufacturer: Freescale Semiconductor / Motorola

Oscillator Options
On the HCS12 D-family there are three oscillator options:
On the D-family, a 5 V level on Port E.7 (/XCLKS) at reset will select the Colpitts oscillator option and, as
this pin defaults to having an internal pull-up enabled, the Colpitts configuration is the default if this pin is
unconnected.
S12Dx Oscillator Options — Technical Comparison
The following table compares features of the low power, amplitude controlled Colpitts oscillator and the
full swing, high drive Pierce oscillator:
Freescale Semiconductor
•
•
•
Low power, amplitude controlled Colpitts configuration.
Full swing (2.5V) Pierce configuration (not available on MC9S12D256x K36N and K79X masks).
External clock source
–
–
–
Uses the same MCU configuration as the Pierce option.
The oscillator is a 2.5 V module so an external clock should be ~2.5 V pk-pk.
When implementing a clock with a 5V ‘canned’ oscillator, add a 50% potential divider to reduce
the clock to 2.5 V.
Feature
Oscillator range
Amplitude control
DC-bias cut cap
Biasing resistor
Damping resistor
Quartz stress
EM emission
EM susceptibility
Current (16 MHz)
Current (4 MHz)
Start time (16 MHz)
Start time (4 MHz)
Margin (16 Mhz)
Margin (4 Mhz)
The polarity of this signal can be different on other HCS12 families – check
with the individual data sheet.
Designing Hardware for the HCS12 D-Family, Rev. 0
Colpitts
500 kHz–16 MHz
yes
may be required
not required
not required
minimal
very low
medium
170 µA
100 µA
1.5 ms
3 ms
300–360
2–2.5 k
CAUTION
Ω
Ω
Pierce
500 kHz–40 MHz
no
not required
required
probably required
damping dependent.
medium–high
low
1100 µA
780 µA
1 ms
1 ms (no damp.)
1.6 k
>> 2 k
Ω
Ω
Oscillator Options
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