Datasheet

Chapter 5 Oscillator (OSCV2)
MC9S12E128 Data Sheet, Rev. 1.07
Freescale Semiconductor 203
Figure 5-2. Pierce Oscillator Connections (XCLKS = 1)
Figure 5-3. External Clock Connections (XCLKS = 1)
5.2.3 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 5-1 lists the state coding of the
sampled XCLKS signal. Refer to the device overview chapter for polarity of the XCLKS pin.
Table 5-1. 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)