MC9S12HZ128VAL Datasheet, PDF (205/692 Pages) Freescale Semiconductor, Inc – MC9S12HZ256 Data Sheet, Rev. 2.05

Chapter 6 Oscillator (OSCV2)
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 6-2. Pierce Oscillator Connections (XCLKS = 1)
EXTAL
MCU
XTAL
CMOS-Compatible
External Oscillator
(V_DDPLL Level)
Not Connected
Figure 6-3. External Clock Connections (XCLKS = 1)
6.2.3 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 6-1 lists the state coding of the
sampled XCLKS signal. Refer to the device overview chapter for polarity of the XCLKS pin.
Table 6-1. Clock Selection Based on XCLKS
XCLKS
0
1
Description
Colpitts oscillator selected
Pierce oscillator/external clock selected
MC9S12HZ256 Data Sheet, Rev. 2.05
Freescale Semiconductor
205