MC68HC908MR8 Datasheet, PDF (128/372 Pages) Motorola, Inc – Microcontrollers

Clock Generator Module (CGM)
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 two writes to the PLL control
register. See 8.4.3 Base Clock Selector Circuit.
PCTL Bits 3–0 — Unimplemented Bits
These bits provide no function and always read as logic 1s.
Technical Data
128
Clock Generator Module (CGM)
MC68HC908MR8 — Rev 4.1
Freescale Semiconductor