mc68hc908gr16 Freescale Semiconductor, Inc, mc68hc908gr16 Datasheet - Page 70

• Manufacturer Part Number: mc68hc908gr16
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
4.5.1 PLL Control Register
The PLL control register (PCTL) contains the interrupt enable and flag bits, the on/off switch, the base
clock selector bit, the prescaler bits, and the VCO power-of-two range selector bits.
PLLIE — PLL Interrupt Enable Bit
PLLF — PLL Interrupt Flag Bit
PLLON — PLL On Bit
BCS — Base Clock Select Bit
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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 a 0. Reset clears the PLLIE 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 a 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.
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 (BCS = 1). (See
Circuit.) Reset sets this bit so that the loop can stabilize as the MCU is powering up.
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
Selector
1 = PLL interrupts enabled
0 = PLL interrupts disabled
1 = Change in lock condition
0 = No change in lock condition
1 = PLL on
0 = PLL off
1 = CGMVCLK divided by two drives CGMOUT
0 = CGMXCLK divided by two drives CGMOUT
Circuit.) Reset clears the BCS bit.
Address:
Do not inadvertently clear the PLLF bit. Any read or read-modify-write
operation on the PLL control register clears the PLLF bit.
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
Reset:
Read:
Write:
$0036
PLLIE
Bit 7
0
= Unimplemented
Figure 4-4. PLL Control Register (PCTL)
PLLF
6
0
MC68HC908GR16 Data Sheet, Rev. 5.0
PLLON
5
1
NOTE
NOTE
BCS
4
0
PRE1
3
0
PRE0
2
0
VPR1
4.3.8 Base Clock Selector
1
0
Freescale Semiconductor
4.3.8 Base Clock
VPR0
Bit 0
0