MC68HC908GR4 MOTOROLA [Motorola, Inc], MC68HC908GR4 Datasheet - Page 106

• Manufacturer Part Number: MC68HC908GR4
• Description: Microcontrollers
• Manufacturer: MOTOROLA [Motorola, Inc]

Clock Generator Module (CGMC)
7.4.6 Programming the PLL
Technical Data
106
NOTE:
The following procedure shows how to program the PLL.
The round function in the following equations means that the real
number should be rounded to the nearest integer number.
1. Choose the desired bus frequency, f
2. Calculate the desired VCO frequency (four times the desired bus
3. Choose a practical PLL (crystal) reference frequency, f
Freescale Semiconductor, Inc.
•
•
•
For More Information On This Product,
Software must wait a given time, t
before selecting the PLL as the clock source to CGMOUT
(BCS = 1).
The LOCK bit is disabled.
CPU interrupts from the CGMC are disabled.
frequency).
the reference clock divider, R. Typically, the reference crystal is
32.768 kHz and R = 1.
Frequency errors to the PLL are corrected at a rate of f
stability and lock time reduction, this rate must be as fast as
possible. The VCO frequency must be an integer multiple of this
rate. The relationship between the VCO frequency, f
reference frequency, f
P, the power of two multiplier, and N, the range multiplier, are
integers.
In cases where desired bus frequency has some tolerance,
choose f
requirements (such as modules which are clocked by CGMXCLK),
cost requirements, or ideally, as high as the specified range
Clock Generator Module (CGMC)
Go to: www.freescale.com
RCLK
to a value determined either by other module
f
VCLKDES
f
VCLK
RCLK
=
, is
=
2
----------- f
P
R
4 f
N
AL
BUSDES
RCLK
, after entering tracking mode
BUSDES
MC68HC908GR8 — Rev 4.0
.
VCLK
RCLK
MOTOROLA
RCLK
, and the
/R. For
, and