Modem SPI Register Descriptions
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
5-15
5.13
CLKO_Ctl - Register 0A
The MC1321x provides the ability to trim the crystal oscillator frequency and an output clock with a
programmable frequency that can be used to drive another device, such as a microcontroller. The field
xtal_trim[7:0], CLKO_Ctl Register 0A, Bits 15-8, alter the capacitive loading to the crystal and affects the
oscillator frequency. See
Chapter 9, “Modem Miscellaneous Functions”
The CLKO frequency is programmed using clko_rate[2:0], CLKO_Ctl Register 0A, Bits 2-0.
lists each setting and its respective frequency.
Table 5-12. CLKO Frequency
clko_rate
CLKO
000
16 MHz
001
8 MHz
010
4 MHz
011
2 MHz
100
1 MHz
101
62.5 kHz
110 (default)
32.786+ kHz = 16 MHz / 488
111
16.393+ kHz = 16 MHz / 976
Register 0A
0x0A
BIT
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
xtal_trim[7:0]
clko_rate[2:0]
TYPE
r/w
r/w
RESET
0
1
1
1
1
1
1
0
1
0
0
0
0
1
1
0
0x7E86
Table 5-13. Register 0A Description
Name
Description
Operation
Bits 7-3
Reserved
Leave default
Bits 15-8
xtal_trim[7:0]
— The crystal oscillator capacitor trim bits warps the
crystal frequency by approximately -0.25 ppm per bit.
0x7E is the default setting and suggested
start point for trimming.
Bits 2-0
clko_rate[2:0]
— The CLKO rate bits select the clock frequency of
the CLKO pin.
.
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