User's Manual

System Overview and Functional Block Descriptions
1320x-QE128EVB Reference Manual, Rev. 0.0
3-8 Freescale Semiconductor
3.7 Clocks
The primary clock source for the 1320x-QE128EVB is supplied by the MC1320x transceiver. The
transceiver requires an accurate 16 MHz reference clock that is supplied via an on-board 16 MHz crystal
oscillator, and in turn, the transceiver typically supplies the clock for the MCU. However, there are options
for the MCU clock usage:
• The default clock source for the QE128 is obtained through MC1320x CLKO programmable
frequency clock output. The RF transceiver reference oscillator is 16 MHz and the mounted crystal
Y1 is a 16 MHz device that meets MC1320x specifications. In turn, CLKO can be enabled to
provide the clock source to the MCU as an external input.
• The QE128 Internal Clock Source (ICS) supplies an optional on-board reference oscillator (32KHz
nominal). With use of the on-board Frequency-locked-loop (FLL), CPU frequencies from 2-50
MHz are available. Precision trimming of the internal reference allows for 0.2% resolution and 2%
deviation over temperature and voltage.
• The module also supports optional use of an external 32.768KHz crystal for the MCU. The
on-board MCU clock amp is used with the 32KHz crystal, and higher CPU and bus clock
frequencies are again synthesized through use of the on-board FLL in the ICS.
The external source of clock is selected by Jumper (J5) (See Section 4.11, “Jumper Selection”).