MCU Internal Clock Generator (ICG)
MC1321x Reference Manual, Rev. 1.6
Freescale Semiconductor
14-19
14.5
ICG Registers and Control Bits
Refer to the direct-page register summary in
for the absolute address
assignments for all ICG registers. This section refers to registers and control bits only by their names. A
Freescale-provided equate or header file is used to translate these names into the appropriate absolute
addresses.
14.5.1
Control Register 1 (C1)
Offset
7
6
5
4
3
2
1
0
Read
HGO
RANGE
REFS
CLKS
OSCSTEN
LOCD
0
Write
Reset
0
1
0
0
0
1
0
0
= Unimplemented or Reserved
Figure 14-10. Control Register 1 (C1)
Table 14-6. C1 Field Descriptions
Field
Description
7
HGO
High Gain Oscillator Select
— The HGO bit is used to select between low-power operation and high-amplitude
operation.
0
Oscillator configured for low power operation.
1
Oscillator configured for high amplitude operation.
6
RANGE
Frequency Range Select
— The RANGE bit controls the oscillator, reference divider, and FLL loop prescaler
multiplication factor (P). It selects one of two reference frequency ranges for the . The RANGE bit is write-once
after a reset. The RANGE bit only has an effect in FLL engaged external and FLL bypassed external modes.
0
Oscillator configured for low frequency range. FLL loop prescale factor P is 64.
1
Oscillator configured for high frequency range. FLL loop prescale factor P is 1.
5
REFS
External Reference Select
— The REFS bit controls the external reference clock source for ICGERCLK. The
REFS bit is write-once after a reset.
0
External clock requested.
1
Oscillator using crystal or resonator requested.
4:3
CLKS
Clock Mode Select
— The CLKS bits control the clock mode. If FLL bypassed external is requested, it will not
be selected until ERCS = 1. If the enters Off Mode, the CLKS bits will remain unchanged.
Writes to the CLKS
bits will not take effect if a previous write is not complete.
The CLKS bits
are writable at any time, unless the first write after a reset was CLKS = 0X, the CLKS bits cannot
be written to 1X until after the next reset (because the EXTAL pin was not reserved).
00 Self-clocked
01 FLL engaged, internal reference
10 FLL bypassed, external reference
11 FLL engaged, external reference
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