mc68hc908ld64 Freescale Semiconductor, Inc, mc68hc908ld64 Datasheet - Page 106

• Manufacturer Part Number: mc68hc908ld64
• Description: M68hc08 Microcontrollers Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

Clock Generator Module (CGM)
8.6.2 PLL Bandwidth Control Register (PBWC)
Data Sheet
106
NOTE:
PLLON — PLL On Bit
BCS — Base Clock Select 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 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.
The PLL bandwidth control register does the following:
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, DCLK1 (BCS = 1). 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,
OSCXCLK, or the VCO clock, CGMVCLK, as the source of the CGM
output, DCLK1. BCS cannot be set while the PLLON bit is clear. After
toggling BCS, it may take up to three OSCXCLK and three CGMVCLK
cycles to complete the transition from one source clock to the other.
During the transition, DCLK1 is held in stasis. Reset and the STOP
instruction clear the BCS bit.
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1 = PLL on
0 = PLL off
1 = DCLK1 driven by CGMVCLK
0 = DCLK1 driven by OSCXCLK
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
Clock Generator Module (CGM)
MC68HC908LD64
Freescale Semiconductor
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Rev. 3.0