
Chapter 11 Oscillator (OSCV2) Block Description
Freescale Semiconductor
MC9S12Q128
345
Rev 1.10
Figure 11-2. Pierce Oscillator Connections (XCLKS = 1)
Figure 11-3. External Clock Connections (XCLKS = 1)
11.2.3
XCLKS — Colpitts/Pierce Oscillator Selection Signal
The XCLKS is an input signal which controls whether a crystal in combination with the internal Colpitts
(low power) oscillator is used or whether the Pierce oscillator/external clock circuitry is used. The XCLKS
signal is sampled during reset with the rising edge of RESET.
Table 11-1 lists the state coding of the
sampled XCLKS signal. Refer to the device overview chapter for polarity of the XCLKS pin.
Table 11-1. Clock Selection Based on XCLKS
XCLKS
Description
0
Colpitts oscillator selected
1
Pierce oscillator/external clock selected
MCU
EXTAL
XTAL
RS*
RB
VSSPLL
Crystal or Ceramic
Resonator
C4
C3
* Rs can be zero (shorted) when used with higher frequency crystals.
Refer to manufacturer’s data.
MCU
EXTAL
XTAL
CMOS-Compatible
External Oscillator
Not Connected
(VDDPLL Level)