MC912DG128A Motorola, MC912DG128A Datasheet - Page 138

• Manufacturer Part Number: MC912DG128A
• Description: Microcontrollers
• Manufacturer: Motorola

Clock Functions
MC68HC912DT128A Rev 2.0
138
EXTALi
EXTAL
XTAL
CONSUMPTION
PROGRAMMABLE
OSCILLATOR
CLOCK DIVIDER
REDUCED
SLOW MODE
SLDV <5:0>
EXTALi
The PLL may be used to run the MCU from a different time base than the
incoming crystal value. It creates an integer multiple of a reference
frequency. For increased flexibility, the crystal clock can be divided by
values in a range of 1 – 8 (in unit steps) to generate the reference
frequency. The PLL can multiply this reference clock in a range of 1 to
64. Although it is possible to set the divider to command a very high clock
frequency, do not exceed the specified bus frequency limit for the MCU.
If the PLL is selected, it will continue to run when in WAIT mode resulting
in more power consumption than normal. To take full advantage of the
reduced power consumption of WAIT mode, turn off the PLL before
going into WAIT. Please note that in this case the PLL stabilization time
applies.
The PLL operation is suspended in STOP mode. After STOP exit
followed by the stabilization time, it resumes operation at the same
frequency, provided the AUTO bit is set.
A passive external loop filter must be placed on the control line (XFC
pad). The filter is a second-order, low-pass filter to eliminate the VCO
input ripple. Values of components in the diagram are dependent upon
the desired VCO operation. See
SLWCLK
Figure 14 PLL Functional Diagram
2
XCLK
PROGRAMMABLE
REFDV <2:0>
REFERENCE
DIVIDER
PROGRAMMABLE
SYN <5:0>
DIVIDER
LOOP
Clock Functions
REFCLK
DIVCLK
DETECTOR
DETECTOR
XFC
PHASE
FILTER
LOCK
LOOP
PDET
description.
VDDPLL
DOWN
UP
LOCK
CPUMP
XFC
PAD
VCO
2
PLLCLK
MOTOROLA
4-clock