
MOTOROLA
Appendix C. Clock and Board Guidelines
C-5
Crystal Oscillator External Components
XTAL pad capacitance is CPAD = ~7 pF
EXTAL pad capacitance is CPAD = ~7 pF
CSOCKET is socket and board trace capacitance
Socket capacitance C <=1pF
Board trace capacitance C <=1pF. This should be low since the crystal must be
located very close to the chip.
C.2.1
KAPWR Filtering
The KAPWR signal is the MPC561/MPC563 keep-alive power. KAPWR is used for the
crystal oscillator circuit, and should be isolated from the noisy supplies. It is recommended
that an RC filter be used on KAPWR, or bypass capacitors that are located as close as
possible to the part.
Figure C-4. RC Filter Example
Figure C-5. Bypass Capacitors Example (Alternative)
C.2.2
PLL External Components
VDDSYN and VSSSYN are the PLL dedicated power supplies. These supplies must be
used only for the PLL and isolated from all other noisy signals in the board. VDDSYN
KAPWR
VSSSYN
KAP 2.6 V
100 nF
<10
Board
MPC56x Device
Note: A filter cut off frequency of 500Hz is recommended, however this will result in a
capacitor size of 33uF using a 10 Ohm resistor. This may be too expensive or large
for the system. In this case the filter shown with cut- off frequency of 160kHz will suffice.
KAPWR
VSSSYN
KAP 2.6 V
100 nF
1 F
Board
MPC56x Device