Datasheet

Chapter 11 Oscillator (OSCV2) Block Description
Freescale Semiconductor MC9S12C-Family / MC9S12GC-Family 345
Rev 01.24
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
V
SSPLL
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
(V
DDPLL
Level)