MC68HC908RK2 Datasheet, PDF (111/232 Pages) Motorola, Inc – Microcontroller Unit

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_NOM) of 307.2 kHz ±25 percent, and an internal clock (ICLK) which is
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
++
+
DIGITAL
LOOP
FILTER
–
––
DIGITALLY
CONTROLLED
OSCILLATOR
DSTG[7:0]
DDIV[3:0]
ICLK
TRIM[7:0]
N[6:0]
FREQUENCY
COMPARATOR
CLOCK GENERATOR
MODULO
N
DIVIDER
NAME
NAME
IBASE
REGISTER BIT
MODULE SIGNAL
Figure 8-2. Internal Clock Generator Block Diagram
MC68HC908RK2 — Rev. 4.0
MOTOROLA
Internal Clock Generator Module (ICG)
Advance Information
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