MC68HC08AZ32A Datasheet, PDF (71/312 Pages) Motorola, Inc – HCMOS Microcontroller Unit

CGM Registers
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 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 0.
Bits 3–0 — Reserved for Test
These bits enable test functions not available in user mode. To ensure software portability from
development systems to user applications, software should write 0s to bits 3–0 when writing to PBWC.
4.5.3 PLL Programming Register
The PLL programming register contains the programming information for the modulo feedback divider
and the programming information for the hardware configuration of the VCO.
Address:
Read:
Write:
Reset:
$001E
Bit 7
6
5
4
3
2
1
MUL7
MUL6
MUL5
MUL4
VRS7
VRS6
VRS5
0
1
1
0
0
1
1
Figure 4-6. PLL Programming Register (PPG)
Bit 0
VRS4
0
MUL7–MUL4 — Multiplier Select Bits
These read/write bits control the modulo feedback divider that selects the VCO frequency multiplier,
N. (See 4.3.2.1 Circuits and 4.3.2.4 Programming the PLL). A value of $0 in the multiplier select bits
configures the modulo feedback divider the same as a value of $1. Reset initializes these bits to $6 to
give a default multiply value of 6. Refer to Table 4-2.
NOTE
The multiplier select bits have built-in protection that prevents them from
being written when the PLL is on (PLLON = 1).
MC68HC08AZ32A Data Sheet, Rev. 2
Freescale Semiconductor
71