User's Manual

1323x-Modular Reference Board
1323x Development Hardware Reference Manual, Rev. 1.0
Freescale Semiconductor 3-7
Figure 3-4. 1323x-MRB RF Circuitry
3.2.2 Clocks
The MC1323x provides for two clocks:
• 32 MHz Reference Oscillator - Figure 3-5 shows the external 32 MHz external crystal Y2. This
mounted crystal must meet the MC1323x specifications. The IEEE 802.15.4 Standard requires that
the frequency be accurate to less that +/-40 ppm.
— Capacitors C10 and C11 provide the bulk of the crystal load capacitance. Onboard trim
capacitors can be programmed to center the frequency. At 25°C, it is desired to have the
frequency accurate to +/-10 ppm or less to allow for temperature variation.
— To measure the 32 MHz oscillator frequency, signal PTD7/XTAL_32MOUT can optionally be
programmed to provide a buffered output clock signal
— The 1323x-MRB has provision for injecting an external 32 MHz clock source as an alternative
to use of the onboard crystal:
– The crystal Y2 should be removed
– Resistors R23, R24, R19, and R20 must be mounted
– C23 must be mounted
– The external 32 MHz source is connected to 2-pin header J8; the frequency accuracy of the
external source must meet the +/-40 ppm of the IEEE 802.15.4
• Optional 32.768 kHz Crystal Oscillator - Provision is also made for a secondary 32.768 kHz crystal
X2 (see Figure 3-6). This oscillator can be used for a low power accurate time base.
— The module comes provided with this Y1 crystal and its load capacitors C4 and C15.
— Load capacitors C4 and C15 provide the entire crystal load capacitance; there is no onboard
trim capacitance.
— The 32 kHz oscillator components are supplied, but un-enabled. Zero-ohm resistors R11 and
R13 enable use of IO signals PTA0 and PTA1 via the IO connector and are supplied as mounted.
These must be unmounted and moved to resistor sites R10 and R12 to enable the 32.768 kHz
crystal and disable PTAO and PTA1.