56F8014_08 Datasheet, PDF (26/124 Pages) Freescale Semiconductor, Inc – 16-bit Digital Signal Controllers

Part 3 OCCS
3.1 Overview
This module provides the system clock, which uses it to generate the various chip clocks. This module also
produces the oscillator clock signals, plus the ADC clock and high-speed peripheral clock.
The on-chip clock synthesis module allows product design using an internal relaxation oscillator to run
56F801X family parts at user-selectable frequencies up to 32MHz.
3.2 Features
The On-Chip Clock Synthesis (OCCS) module interfaces to the oscillator and PLL. The OCCS module
features:
• Internal relaxation oscillator
• Ability to power down the internal relaxation oscillator
• Ability to put the internal relaxation oscillator into a standby mode
• 3-bit postscaler provides control for the PLL output
• Ability to power down the internal PLL
• Provides 2X system clock frequency, which operates at twice the system clock, to the System Integration
Module (SIM) that is used to generate the various device clocks
• Provides 3X system clock, which operates at three times the system clock, to PWM and Timer
• Safety shutdown feature is available in the event that the PLL reference clock disappears
• Can be driven from an external clock source
The clock generation module provides the programming interface for both the PLL and internal relaxation
oscillator.
3.3 Operating Modes
In 56F801X family parts, either an internal oscillator or an external frequency source can be used to
provide a reference clock to the SIM.
The 2X system clock source output from the OCCS can be described by one of the following equations:
2X system frequency = oscillator frequency
2X system frequency = (oscillator frequency X 8) / (postscaler)
where:
postscaler = 1, 2, 4, 8, 16, or 32 PLL output divider
The SIM is responsible for further dividing these frequencies by two, which will insure a 50% duty cycle
in the system clock output.
56F8014 Technical Data, Rev. 11
26
Freescale Semiconductor