MC9S12C Datasheet, PDF (345/680 Pages) Motorola, Inc – 16-Bit Microcontroller

Chapter 11 Oscillator (OSCV2) Block Description
EXTAL
MCU
XTAL
RB
RS*
C3
Crystal or Ceramic
Resonator
C4
V_SSPLL
* Rs can be zero (shorted) when used with higher frequency crystals.
Refer to manufacturer’s data.
Figure 11-2. Pierce Oscillator Connections (XCLKS = 1)
EXTAL
MCU
XTAL
CMOS-Compatible
External Oscillator
(V_DDPLL Level)
Not Connected
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
0
1
Description
Colpitts oscillator selected
Pierce oscillator/external clock selected
Freescale Semiconductor
MC9S12C-Family / MC9S12GC-Family
345
Rev 01.23