Datasheet

Clock Generator Module (CGM)
MC68HC908GR16 Data Sheet, Rev. 5.0
72 Freescale Semiconductor
4.5.2 PLL Bandwidth Control Register
The PLL bandwidth control register (PBWC):
• Selects automatic or manual (software-controlled) bandwidth control mode
• Indicates when the PLL is locked
• In automatic bandwidth control mode, indicates when the PLL is in acquisition or tracking mode
• In manual operation, forces the PLL into acquisition or tracking mode
AUTO — Automatic Bandwidth Control Bit
This read/write bit selects automatic or manual bandwidth control. When initializing the PLL for manual
operation (AUTO = 0), clear the ACQ
bit before turning on the PLL. Reset clears the AUTO bit.
1 = Automatic bandwidth control
0 = Manual bandwidth control
LOCK — Lock Indicator Bit
When the AUTO bit is set, LOCK is a read-only bit that becomes set when the VCO clock, CGMVCLK,
is locked (running at the programmed frequency). When the AUTO bit is clear, LOCK reads as a 0 and
has no meaning. The write one function of this bit is reserved for test, so this bit must always be written
a 0. Reset clears the LOCK bit.
1 = VCO frequency correct or locked
0 = VCO frequency incorrect or unlocked
ACQ
— Acquisition Mode Bit
When the AUTO bit is set, ACQ
is a read-only bit that indicates whether the PLL is in acquisition mode
or tracking mode. When the AUTO bit is clear, ACQ
is a read/write bit that controls whether the PLL is
in acquisition or tracking mode.
In automatic bandwidth control mode (AUTO = 1), the last-written value from manual operation is
stored in a temporary location and is recovered when manual operation resumes. Reset clears this bit,
enabling acquisition mode.
1 = Tracking mode
0 = Acquisition mode
Address: $0037
Bit 7654321Bit 0
Read:
AUTO
LOCK
ACQ
0000
R
Write:
Reset:00000000
= Unimplemented R = Reserved
Figure 4-5. PLL Bandwidth Control Register (PBWC)