MC68HC08AS32 Datasheet, PDF (101/394 Pages) Motorola, Inc – M68HC08 Family of 8-bit microcontroller units (MCUs)

Clock Generator Module (CGM)
Functional Description
• Software must wait a given time, t_AL, after entering tracking mode
before selecting the PLL as the clock source to CGMOUT
(BCS = 1).
• The LOCK bit is disabled.
• CPU interrupts from the CGM are disabled.
8.4.2.4 Programming the PLL
Use this procedure to program the PLL:
1. Choose the desired bus frequency, f_BUSDES.
Example: f_BUSDES = 8 MHz
2. Calculate the desired VCO frequency, f_VCLKDES.
f_VCLKDES = 4 × f_BUSDES
Example: f_VCLKDES = 4 × 8 MHz = 32 MHz
3. Using a reference frequency, f_RCLK, equal to the crystal frequency,
calculate the VCO frequency multiplier, N.
NOTE: The round function means that the result is rounded to the nearest
integer.
N
=
r
ou
nd


-f-^V---f^C--_R--^L-_C-^K--_L-^D--_K-^E---^S-_
Example: N = ^{3--4--2---M--M---H--H---z-z--} = 8
4. Calculate the VCO frequency, f_VCLK.
f_VCLK = N × f_RCLK
Example: f_VCLK = 8 × 4 MHz = 32 MHz
MC68HC08AS32 — Rev. 3.0
MOTOROLA
Clock Generator Module (CGM)
Advance Information
101