AN2727 Freescale Semiconductor / Motorola, AN2727 Datasheet - Page 20

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

S12 CRG — Colpitts Oscillator
S12 CRG — Colpitts Oscillator
500 kHz to 16 MHz low power oscillator: 1 V pk-pk with DC offset.
On the D-family, pull XCLKS pin high at reset.
Values for C
Additional Colpitts Oscillator Layout Considerations
A key consideration for the Colpitts configuration is to minimize the parasitic loading of the EXTAL track
to ground. Keep the EXTAL track as short as possible and tracked away from other signals, especially
ground.
20
DC
, C
1
and C
* Possible d.c. blocking capacitor (C
to eliminate 1.1V DC bias. Check with crystal manufacturer.
2
should be confirmed with the crystal or resonator manufacturer.
Figure 6. Colpitts Oscillator Configuration
Designing Hardware for the HCS12 D-Family, Rev. 0
MCU
EXTAL
XTAL
C
dc
*
dc
C
) needed for some vendors’ crystals
1
C
2
Crystal or
ceramic resonator
Freescale Semiconductor