
Clock Generator Module (CGM)
MC68HC908GR60A MC68HC908GR48A MC68HC908GR32A Data Sheet, Rev. 1
80
Freescale Semiconductor
4.4.9 CGM Base Clock Output (CGMOUT)
CGMOUT is the clock output of the CGM. This signal goes to the SIM, which generates the MCU clocks.
CGMOUT is a 50 percent duty cycle clock running at twice the bus frequency. CGMOUT is software
programmable to be either the oscillator output, CGMXCLK, divided by two or the VCO clock, CGMVCLK,
divided by two.
4.4.10 CGM CPU Interrupt (CGMINT)
CGMINT is the interrupt signal generated by the PLL lock detector.
4.5 CGM Registers
These registers control and monitor operation of the CGM:
PLL control register (PCTL) — see
4.5.1 PLL Control Register
PLL bandwidth control register (PBWC) — see
4.5.2 PLL Bandwidth Control Register
PLL multiplier select register high (PMSH) — see
4.5.3 PLL Multiplier Select Register High
PLL multiplier select register low (PMSL) — see
4.5.4 PLL Multiplier Select Register Low
PLL VCO range select register (PMRS) — see
4.5.5 PLL VCO Range Select Register
Figure 4-3
is a summary of the CGM registers.
Addr.
Register Name
Bit 7
6
5
4
3
2
1
Bit 0
$0036
PLL Control Register
(PCTL)
See page 81.
Read:
Write:
Reset:
Read:
Write:
Reset:
Read:
Write:
Reset:
Read:
Write:
Reset:
Read:
Write:
Reset:
Read:
Write:
Reset:
PLLIE
PLLF
PLLON
BCS
R
R
VPR1
VPR0
0
0
1
0
0
0
0
0
0
0
0
0
$0037
PLL Bandwidth Control
Register (PBWC)
See page 82.
AUTO
LOCK
ACQ
R
0
0
0
0
0
0
0
0
0
0
0
0
$0038
PLL Multiplier Select High
Register (PMSH)
See page 83.
MUL11
MUL10
MUL9
MUL8
0
0
0
0
0
0
0
0
$0039
PLL Multiplier Select Low
Register (PMSL)
See page 84.
MUL7
MUL6
MUL5
MUL4
MUL3
MUL2
MUL1
MUL0
0
1
0
0
0
0
0
0
$003A
PLL VCO Select Range
Register (PMRS)
See page 84.
VRS7
VRS6
VRS5
VRS4
VRS3
VRS2
VRS1
VRS0
0
0
1
0
0
0
0
0
0
0
0
0
$003B
Reserved Register
R
R
R
R
0
0
0
0
R
0
0
0
1
= Unimplemented
= Reserved
NOTES:
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 4-3. CGM I/O Register Summary