Functional Description
Addr.
Register Name
Bit 7
PLLIE
0
6
5
PLLON
1
4
3
2
1
Bit 0
VPR0
0
Read:
Write:
Reset:
Read:
PLLF
BCS
PRE1
PRE0
VPR1
PLL Control Register
(PTCL)
$0036
0
0
0
0
0
0
0
0
0
LOCK
PLL Bandwidth Control
AUTO
ACQ
R
$0037
Register Write:
(PBWC)
Reset:
Read:
0
0
0
0
0
0
0
0
0
MUL11
0
0
MUL10
0
0
MUL9
0
PLL Multiplier Select
MUL8
$0038
Register High Write:
(PMSH)
Reset:
Read:
0
0
0
0
0
MUL0
0
PLL Multiplier Select
MUL7
0
MUL6
1
MUL5
0
MUL4
0
MUL3
0
MUL2
0
MUL1
0
$0039
Register Low Write:
(PMSL)
Reset:
Read:
PLL VCO Range Select
VRS7
VRS6
VRS5
VRS4
VRS3
0
VRS2
0
VRS1
0
VRS0
0
$003A
$003B
NOTES:
Register Write:
(PMRS)
Reset:
Read:
0
0
1
0
0
0
0
0
PLL Reference Divider
RDS3
RDS2
RDS1
0
RDS0
1
Select Register Write:
(PMDS)
Reset:
0
0
0
0
0
0
= Reserved
= Unimplemented
R
1. When AUTO = 0, PLLIE is forced clear and is read-only.
2. When AUTO = 0, PLLF and LOCK read as clear.
3. When AUTO = 1, ACQ is read-only.
4. When PLLON = 0 or VRS7:VRS0 = $0, BCS is forced clear and is read-only.
5. When PLLON = 1, the PLL programming register is read-only.
6. When BCS = 1, PLLON is forced set and is read-only.
Figure 6-2. CGM I/O Register Summary
6.3.1 Oscillator Module
The oscillator module provides two clock outputs CGMXCLK and CGMRCLK to the CGM module.
CGMXCLK when selected, is driven to SIM module to generate the system bus clock. CGMRCLK is used
by the phase-lock-loop to provide a higher frequency system bus clock. The oscillator module also
provides the reference clock for the timebase module (TBM). See Chapter 5 Oscillator (OSC) for detailed
oscillator circuit description. See Chapter 10 Timebase Module (TBM) for detailed description on TBM.
6.3.2 Phase-Locked Loop Circuit (PLL)
The PLL is a frequency generator that can operate in either acquisition mode or tracking mode, depending
on the accuracy of the output frequency. The PLL can change between acquisition and tracking modes
either automatically or manually.
6.3.3 PLL Circuits
The PLL consists of these circuits:
•
•
•
•
Voltage-controlled oscillator (VCO)
Reference divider
Frequency pre-scaler
Modulo VCO frequency divider
MC68HC908AP Family Data Sheet, Rev. 4
Freescale Semiconductor
81
FREESCALE [ Freescale ]
