Freescale Semiconductor, Inc.
Internal Clock Generator Module (ICG)
Functional Description
8.4.2 Internal Clock Generator
The internal clock generator, shown in Figure 8-2, creates a low-
frequency base clock (IBASE), which operates at a nominal frequency
(f ) of 307.2 kHz ±25 percent, and an internal clock (ICLK) which is
NOM
an integer multiple of IBASE. This multiple is the ICG multiplier factor
(N), which is programmed in the ICG multiplier register (ICGMR). The
internal clock generator is turned off and the output clocks (IBASE and
ICLK) are held low when the internal clock generator enable signal
(ICGEN) is clear.
The internal clock generator contains:
•
•
•
A digitally controlled oscillator
A modulo N divider
A frequency comparator, which contains voltage and current
references, a frequency to voltage converter, and comparators
•
A digital loop filter
ICGEN
VOLTAGE &
CURRENT
REFERENCES
++
DSTG[7:0]
DDIV[3:0]
+
DIGITAL
LOOP
FILTER
DIGITALLY
CONTROLLED
OSCILLATOR
–
ICLK
– –
TRIM[7:0]
N[6:0]
FREQUENCY
COMPARATOR
MODULO
N
CLOCK GENERATOR
DIVIDER
IBASE
NAME
NAME
REGISTER BIT
MODULE SIGNAL
Figure 8-2. Internal Clock Generator Block Diagram
MC68HC908RFRK2
MOTOROLA
AdvanceInformation
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Internal Clock Generator Module (ICG)
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