
Chapter 6 Oscillator (OSCV2)
MC9S12HZ256 Data Sheet, Rev. 2.04
204
Freescale Semiconductor
6.2
External Signal Description
This section lists and describes the signals that connect off chip.
6.2.1
V
DDPLL
and V
SSPLL
— PLL Operating Voltage, PLL Ground
These pins provide the operating voltage (V
DDPLL
) and ground (V
SSPLL
) for the OSC circuitry. This
allows the supply voltage to the OSC to be independently bypassed.
6.2.2
EXTAL and XTAL — Clock/Crystal Source Pins
These pins provide the interface for either a crystal or a CMOS compatible clock to control the internal
clock generator circuitry. EXTAL is the external clock input or the input to the crystal oscillator amplifier.
XTAListheoutputofthecrystaloscillatoramplifier.AlltheMCUinternalsystemclocksarederivedfrom
the EXTAL input frequency. In full stop mode (PSTP = 0) the EXTAL pin is pulled down by an internal
resistor of typical 200 k
.
NOTE
Freescale Semiconductor recommends an evaluation of the application
board and chosen resonator or crystal by the resonator or crystal supplier
.
The Crystal circuit is changed from standard.
The Colpitts circuit is not suited for overtone resonators and crystals.
Figure 6-1. Colpitts Oscillator Connections (XCLKS = 0)
NOTE
The Pierce circuit is not suited for overtone resonators and crystals without
a careful component selection.
MCU
C2
EXTAL
XTAL
V
SSPLL
C1
CDC*
Crystal or Ceramic
Resonator
* Due to the nature of a translated ground Colpitts oscillator
a DC voltage bias is applied to the crystal.
Please contact the crystal manufacturer for crystal DC bias
conditions and recommended capacitor value CDC.