mc68hc708mp16 Freescale Semiconductor, Inc, mc68hc708mp16 Datasheet - Page 120

• Manufacturer Part Number: mc68hc708mp16
• Description: M68hc08 Microcontrollers
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
Technical Data
120
ACQ — Acquisition Mode Bit
XLD — Crystal Loss Detect Bit
PBWC[3:0] — Reserved for Test
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.
When the VCO output, CGMVCLK, is driving CGMOUT, this
read/write bit can indicate whether the crystal reference frequency is
active or not. 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.
The crystal loss detect function works only when the BCS bit is set,
selecting CGMVCLK to drive CGMOUT. When BCS is clear, XLD
always reads as logic 0.
These bits enable test functions not available in user mode. To ensure
software portability from development systems to user applications,
software should write zeros to PBWC[3:0] whenever writing to PBWC.
1 = Tracking mode
0 = Acquisition mode
1 = Crystal reference is not active
0 = Crystal reference is active
Clock Generator Module (CGM)
MC68HC708MP16
Freescale Semiconductor
—
Rev. 3.1