Datasheet
Table Of Contents
- Part 1 Overview
- Part 2 Signal/Connection Descriptions
- 2.1 Introduction
- 2.2 Power and Ground Signals
- 2.3 Clock and Phase Locked Loop Signals
- 2.4 Address, Data, and Bus Control Signals
- 2.5 Interrupt and Program Control Signals
- 2.6 GPIO Signals
- 2.7 Pulse Width Modulator (PWM) Signals
- 2.8 Serial Peripheral Interface (SPI) Signals
- 2.9 Quadrature Decoder Signals
- 2.10 Serial Communications Interface (SCI) Signals
- 2.11 CAN Signals
- 2.12 Analog-to-Digital Converter (ADC) Signals
- 2.13 Quad Timer Module Signals
- 2.14 JTAG/OnCE
- Part 3 Specifications
- 3.1 General Characteristics
- 3.2 DC Electrical Characteristics
- 3.3 AC Electrical Characteristics
- 3.4 Flash Memory Characteristics
- 3.5 External Clock Operation
- 3.6 External Bus Asynchronous Timing
- 3.7 Reset, Stop, Wait, Mode Select, and Interrupt Timing
- 3.8 Serial Peripheral Interface (SPI) Timing
- 3.9 Quad Timer Timing
- 3.10 Quadrature Decoder Timing
- 3.11 Serial Communication Interface (SCI) Timing
- 3.12 Analog-to-Digital Converter (ADC) Characteristics
- 3.13 Controller Area Network (CAN) Timing
- 3.14 JTAG Timing
- Part 4 Packaging
- Part 5 Design Considerations
- Part 6 Ordering Information
External Clock Operation
56F805 Technical Data, Rev. 16
Freescale Semiconductor 29
as a typical circuit board trace capacitance the parallel load capacitance presented to the crystal is 9pF as
determined by the following equation:
This is the value load capacitance that should be used when selecting a crystal and determining the actual
frequency of operation of the crystal oscillator circuit.
Figure 3-7 Connecting to a Crystal Oscillator
3.5.2 Ceramic Resonator
It is also possible to drive the internal oscillator with a ceramic resonator, assuming the overall system
design can tolerate the reduced signal integrity. In Figure 3-8, a typical ceramic resonator circuit is shown.
Refer to supplier’s recommendations when selecting a ceramic resonator and associated components. The
resonator and components should be mounted as close as possible to the EXTAL and XTAL pins. The
internal 56F80x oscillator circuitry is designed to have no external load capacitors present. As shown in
Figure 3-7 no external load capacitors should be used.
Figure 3-8 Connecting a Ceramic Resonator
Note: Freescale recommends only two terminal ceramic resonators vs. three terminal resonators
(which contain an internal bypass capacitor to ground).
CL =
CL1 * CL2
CL1 + CL2
+ Cs =
+ 3 = 6 + 3 = 9pF
12 * 12
12 + 12
Recommended External Crystal
Parameters:
R
z
= 1 to 3 MΩ
f
c
= 8MHz (optimized for 8MHz)
EXTAL XTAL
R
z
f
c
Recommended Ceramic Resonator
Parameters:
R
z
= 1 to 3 MΩ
f
c
= 8MHz (optimized for 8MHz)
EXTAL XTAL
R
z
f
c