
Clock Generator Module (CGM)
MC68HC908GR60A MC68HC908GR48A MC68HC908GR32A Data Sheet, Rev. 5
82
Freescale Semiconductor
if the PLL is off. Therefore, PLLON cannot be cleared when BCS is set, and
BCS cannot be set when PLLON is clear. If the PLL is off (PLLON = 0),
selecting CGMVCLK requires two writes to the PLL control register. (See
VPR1 and VPR0 — VCO Power-of-Two Range Select Bits
These read/write bits control the VCO’s hardware power-of-two range multiplier E that, in conjunction
with L controls the hardware center-of-range frequency, fVRS. VPR1:VPR0 cannot be written when the
NOTE
Verify that the value of the VPR1 and VPR0 bits in the PCTL register are
appropriate for the given reference and VCO clock frequencies before
on selecting the proper value for these control bits.
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
Table 4-4. VPR1 and VPR0 Programming
VPR1 and VPR0
E
VCO Power-of-Two
Range Multiplier
00
0
1
01
1
2
10
2(1)
1. Do not program E to a value of 3.
4
Address:
$0037
Bit 7
654321
Bit 0
Read:
AUTO
LOCK
ACQ
0000
R
Write:
Reset:
00000000
= Unimplemented
R
= Reserved
Figure 4-5. PLL Bandwidth Control Register (PBWC)