S912XEG128J2MAA Datasheet, PDF (88/1324 Pages) Freescale Semiconductor, Inc – Microcontrollers

Chapter 1 Device Overview MC9S12XE-Family
1.13 Oscillator Configuration
The XCLKS is an input signal which controls whether a crystal in combination with the internal loop
controlled (low power) Pierce oscillator is used or whether full swing Pierce oscillator/external clock
circuitry is used. For this device XCLKS is mapped to PE7.
The XCLKS signal selects the oscillator configuration during reset low phase while a clock quality check
is ongoing. This is the case for:
• Power on reset or low-voltage reset
• Clock monitor reset
• Any reset while in self-clock mode or full stop mode
The selected oscillator configuration is frozen with the rising edge of the RESET pin in any of these above
described reset cases.
EXTAL
MCU
C₁
Crystal or
Ceramic Resonator
XTAL
C₂
V_SSPLL
Figure 1-10. Loop Controlled Pierce Oscillator Connections (XCLKS = 1)
EXTAL
MCU
XTAL
R_B
R_S
C₁
Crystal or
Ceramic Resonator
R_B=1MΩ
;
R_S
specified
by
crystal
C₂
vendor
V_SSPLL
Figure 1-11. Full Swing Pierce Oscillator Connections (XCLKS = 0)
EXTAL
MCU
XTAL
CMOS-Compatible
External Oscillator
Not Connected
Figure 1-12. External Clock Connections (XCLKS = 0)
MC9S12XE-Family Reference Manual Rev. 1.25
88
Freescale Semiconductor