Chapter 11 Oscillator (OSCV2) Block Description
344
MC9S12C-Family / MC9S12GC-Family
Freescale Semiconductor
Rev 01.24
11.2
External Signal Description
This section lists and describes the signals that connect off chip.
11.2.1
V
DDPLL
and V
SSPLL
— PLL Operating Voltage, PLL Ground
These pins provide the operating voltage (V
DDPLL
) and ground (V
SSPLL
) for the OSCV2 circuitry. This
allows the supply voltage to the OSCV2 to be independently bypassed.
11.2.2
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.
XTAL is the output of the crystal oscillator amplifier. All the MCU internal system clocks are derived from
the EXTAL input frequency. In full stop mode (PSTP = 0) the EXTAL pin is pulled down by an internal
resistor of typical 200 k
Ω
.
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 11-1. 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.
Summary of Contents for MC9S12C Family
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