MC68HC908AT32 Datasheet, PDF (103/378 Pages) Freescale Semiconductor, Inc – Microcontrollers

CGM Registers
8.5.2 PLL Bandwidth Control Register
The PLL bandwidth control register:
• 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
Address: $001D
Bit 7
6
5
4
3
2
1
Bit 0
Read:
LOCK
0
0
0
0
AUTO
ACQ
XLD
Write:
Reset: 0
0
0
0
0
0
0
0
= Unimplemented
Figure 8-5. PLL Bandwidth Control Register (PBWC)
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 logic 0
and has no meaning. 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
XLD — Crystal Loss Detect Bit
When the VCO output, CGMVCLK, is driving CGMOUT, this read/write bit can indicate whether the
crystal reference frequency is active or not.
1 = Crystal reference not active
0 = Crystal reference active
To check the status of the crystal reference, do the following:
1. Write a logic 1 to XLD.
2. Wait N × 4 cycles. N is the VCO frequency multiplier.
3. Read XLD.
MC68HC908AT32 Data Sheet, Rev. 3.1
Freescale Semiconductor
103