Clock Generator Module (CGM)
CGM Registers
MC68HC908GR60A MC68HC908GR48A MC68HC908GR32A
Data Sheet
MOTOROLA
Clock Generator Module (CGM)
91
PLLIE — PLL Interrupt Enable Bit
This read/write bit enables the PLL to generate an interrupt request when the
LOCK bit toggles, setting the PLL flag, PLLF. When the AUTO bit in the PLL
bandwidth control register (PBWC) is clear, PLLIE cannot be written and reads
as 0. Reset clears the PLLIE bit.
1 = PLL interrupts enabled
0 = PLL interrupts disabled
PLLF — PLL Interrupt Flag Bit
This read-only bit is set whenever the LOCK bit toggles. PLLF generates an
interrupt request if the PLLIE bit also is set. PLLF always reads as 0 when the
AUTO bit in the PLL bandwidth control register (PBWC) is clear. Clear the PLLF
bit by reading the PLL control register. Reset clears the PLLF bit.
1 = Change in lock condition
0 = No change in lock condition
NOTE:
Do not inadvertently clear the PLLF bit. Any read or read-modify-write operation on
the PLL control register clears the PLLF bit.
PLLON — PLL On Bit
This read/write bit activates the PLL and enables the VCO clock, CGMVCLK.
PLLON cannot be cleared if the VCO clock is driving the base clock, CGMOUT
the loop can stabilize as the MCU is powering up.
1 = PLL on
0 = PLL off
BCS — Base Clock Select Bit
This read/write bit selects either the crystal oscillator output, CGMXCLK, or the
VCO clock, CGMVCLK, as the source of the CGM output, CGMOUT. CGMOUT
frequency is one-half the frequency of the selected clock. BCS cannot be set
while the PLLON bit is clear. After toggling BCS, it may take up to three
CGMXCLK and three CGMVCLK cycles to complete the transition from one
source clock to the other. During the transition, CGMOUT is held in stasis. (See
1 = CGMVCLK divided by two drives CGMOUT
0 = CGMXCLK divided by two drives CGMOUT
NOTE:
PLLON and BCS have built-in protection that prevents the base clock selector
circuit from selecting the VCO clock as the source of the base clock 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
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 PLLON bit is set. Reset clears