PXD20RM Datasheet, PDF (227/1628 Pages) Freescale Semiconductor, Inc – PXD20 Microcontroller

NOTE
This low-power loop-controlled circuit is not suited for overtone resonators
and crystals.
Freescale recommends an evaluation of the layout and performance of the
application board and chosen resonator or crystal by the resonator or crystal
supplier. The low-power nature of the circuit should be noted when
performing this evaluation since the impact of stray capacitance and
external disturbances can be larger than seen with higher power oscillators.
EXTAL
MCU
C1
Crystal or
Ceramic Resonator
XTAL
C2
V_SSPLL
Figure 8-27. Loop controlled Pierce oscillator connections (LCP mode selected)
EXTAL
MCU
XTAL
CMOS Compatible
External Oscillator
(V_DDPLL Level)
Not Connected
Figure 8-28. External clock connections
8.4.1.6 Memory map and register definition
The FXOSC does not contain any configuration registers. The oscillator is enabled and disabled using the
Mode Entry module.
8.4.1.7 Functional description
The FXOSC module has control circuitry to maintain the crystal oscillator circuit voltage level to an
optimal level which is determined by the amount of hysteresis being used and the maximum oscillation
range.
The oscillator block has two external pins, EXTAL and XTAL. The oscillator input pin, EXTAL, is
intended to be connected to either a crystal or an external clock source. The XTAL pin is an output signal
that provides crystal circuit feedback.
Freescale Semiconductor
PXD20 Microcontroller Reference Manual, Rev. 1
Preliminary—Subject to Change Without Notice
8-31