User's Manual

System Overview and Functional Block Descriptions
1322x-LPB Reference Manual, Rev. 1.1
Freescale Semiconductor 3-7
3.5 Clock Sources
The 1322x-LPB supports two primary clock sources for the MC1322x.
3.5.1 Reference Oscillator (24 MHz nominal)
The reference oscillator is the primary source for all internal MC1322x clocks. Figure 3-8 shows the LPB
circuitry related to the reference oscillator. The default frequency for the reference oscillator is 24 MHz
and the mounted crystal X1 is a 24 MHz device that meets MC1322x specifications. There are two
additional options for the module:
• X1 can be replaced by a 13-26 MHz crystal - It must meet MC1322x specifications. In addition,
the onboard PLL must be used in this case. The PCB provides for the PLL filter components, but
these are not populated. To use a non-standard crystal, the PLL filter components of R5, C4, and
C5 must be populated. Also, software must enable use of the PLL for the internal modem clock.
• An external clock source can be supplied as the reference source - This is typically 24 MHz. The
frequency must be accurate to +/-40ppm. The external clock source can supplied via test point
TP86 and C57 (10 pF) must also be installed.
Figure 3-8. Reference Oscillator Related Circuitry
C58
10pF
Not Mounted
R73
1K
Not Mounted
VCC
R72
1K
Not Mounted
C57
10pF
Not Mounted
TP1
TP9
X1
24.00MHz
External
Clock
Source
TP87
TP86
R5
240R
Not Mounted
C5
180nF
Not Mounted
C4
27nF
Not Mounted
RF_PLL_FLT
XTAL_24_OUT
XTAL_24_IN
PLL External Filter