Datasheet

Introduction
56F8357 Technical Data, Rev. 15
Freescale Semiconductor 39
Preliminary
Part 3 On-Chip Clock Synthesis (OCCS)
3.1 Introduction
Refer to the OCCS chapter of the 56F8300 Peripheral User Manual for a full description of the OCCS.
The material contained here identifies the specific features of the OCCS design. Figure 3-1 shows the
specific OCCS block diagram to reference from the OCCS chapter of the 56F8300 Peripheral User
Manual.
Figure 3-1 OCCS Block Diagram
3.2 External Clock Operation
The system clock can be derived from an external crystal, ceramic resonator, or an external system clock
signal. To generate a reference frequency using the internal oscillator, a reference crystal or ceramic
resonator must be connected between the EXTAL and XTAL pins.
3.2.1 Crystal Oscillator
The internal oscillator is also designed to interface with a parallel-resonant crystal resonator in the
frequency range specified for the external crystal in Table 10-13. A recommended crystal oscillator circuit
is shown in Figure 3-2. Follow the crystal supplier’s recommendations when selecting a crystal, since
MUX
EXTAL
XTAL
FEEDBACK
LCK
Prescaler CLK
Postscaler CLK
F
OUT/2
Crystal
OSC
Loss of
Reference
Clock
Detector
Lock
Detector
ZSRC
Bus Interface & Control
F
OUT
F
REF
PLLDB
PLLCOD
PLLCID
Bus
Interface
Loss of Reference
Clock Interrupt
SYS_CLK2
Source to SIM
MUX
CLKMODE
÷2
Prescaler
÷ (1,2,4,8)
Postscaler
÷ (1,2,4,8)
MSTR_OSC
PLL
x (1 to 128)