XC908AS60ACFU Motorola Semiconductor Products, XC908AS60ACFU Datasheet - Page 175

• Manufacturer Part Number: XC908AS60ACFU
• Description: MC68HC908AZ60A, MC68HC908AS60A Hcmos Microcontroller Unit Technical Data
• Manufacturer: Motorola Semiconductor Products

10.4.2.2 Acquisition and Tracking Modes
10.4.2.3 Manual and Automatic PLL Bandwidth Modes
MC68HC908AZ60A — Rev 2.0
MOTOROLA
The PLL filter is manually or automatically configurable into one of two
operating modes:
The PLL can change the bandwidth or operational mode of the loop filter
manually or automatically.
In automatic bandwidth control mode (AUTO = 1), the lock detector
automatically switches between acquisition and tracking modes.
Automatic bandwidth control mode also is used to determine when the
VCO clock, CGMVCLK, is safe to use as the source for the base clock,
CGMOUT. See
CPU interrupt requests are enabled, the software can wait for a PLL
CPU interrupt request and then check the LOCK bit. If CPU interrupts
are disabled, software can poll the LOCK bit continuously (during PLL
startup, usually) or at periodic intervals. In either case, when the LOCK
bit is set, the VCO clock is safe to use as the source for the base clock.
See
as the source for the base clock and the LOCK bit is clear, the PLL has
suffered a severe noise hit and the software must take appropriate
action, depending on the application. See
•
•
Base Clock Selector Circuit
Acquisition mode — In acquisition mode, the filter can make large
frequency corrections to the VCO. This mode is used at PLL
startup or when the PLL has suffered a severe noise hit and the
VCO frequency is far off the desired frequency. When in
acquisition mode, the ACQ bit is clear in the PLL bandwidth control
register. See
Tracking mode — In tracking mode, the filter makes only small
corrections to the frequency of the VCO. PLL jitter is much lower
in tracking mode, but the response to noise is also slower. The
PLL enters tracking mode when the VCO frequency is nearly
correct, such as when the PLL is selected as the base clock
source. See
is automatically in tracking mode when it’s not in acquisition mode
or when the ACQ bit is set.
Clock Generator Module (CGM)
PLL Bandwidth Control Register
Base Clock Selector Circuit
PLL Bandwidth Control Register
on page 179. If the VCO is selected
Interrupts
Clock Generator Module (CGM)
on page 179. The PLL
on page 185. If PLL
Functional Description
on page 189.
on page 185.
Technical Data
175