s908az32ag2cfue Freescale Semiconductor, Inc, s908az32ag2cfue Datasheet - Page 95

• Manufacturer Part Number: s908az32ag2cfue
• Description: M68hc08 Microcontrollers 8-bit Microcontroller
• Manufacturer: Freescale Semiconductor, Inc

The PLL also can operate in manual mode (AUTO = 0). Manual mode is used by systems that do not
require an indicator of the lock condition for proper operation. Such systems typically operate well below
f
8.3.2.4 Programming the PLL
Use this 9-step procedure to program the PLL. The table below lists the variables used and their meaning
(Please also reference
Freescale Semiconductor
busmax
1. Choose the desired bus frequency, f
2. Calculate the desired VCO frequency, f
3. Using a reference frequency, f
•
•
•
•
•
ACQ is a writable control bit that controls the mode of the filter. Before turning on the PLL in manual
mode, the ACQ bit must be clear.
Before entering tracking mode (ACQ = 1), software must wait a given time, t
Electrical
(PCTL).
Software must wait a given time, t
clock source to CGMOUT (BCS = 1).
The LOCK bit is disabled.
CPU interrupts from the CGM are disabled.
Example: f
f
Example: f
multiplier, N. Round the result to the nearest integer.
VCLKDES
and require fast startup. The following conditions apply when in manual mode:
= 4 × f
Specifications), after turning on the PLL by setting PLLON in the PLL control register
BUSDES
VCLKDES
f
f
Variable
f
f
CGMRCLK
CGMVCLK
f
VCLKDES
CGMVRS
BUSDES
f
f
NOM
BUS
BUSDES
Figure
= 8 MHz
= 4 × 8 MHz = 32 MHz
8-1).
MC68HC908AZ32A Data Sheet, Rev. 2
Desired Bus Clock Frequency
Desired VCO Clock Frequency
Chosen Reference Crystal Frequency
Calculated VCO Clock Frequency
Calculated Bus Clock Frequency
Nominal VCO Center Frequency
Shifted VCO Center Frequency
Table 8-2. Variable Definitions
Example:
RCLK
al
N
, equal to the crystal frequency, calculate the VCO frequency
, after entering tracking mode before selecting the PLL as the
BUSDES
=
VCLKDES
-------------------------
f
f
N
CGMRCLK
VCLKDES
=
.
32 MHz
------------------- -
4 MHz
.
Definition
=
8
acq
Functional Description
(see
Chapter 25
95