1
Getting Started - Oscillators
© 3.6.2001
Oscillator
Oscillator
Oscillator
Overview, Design Tips and
Troubleshooting of the PICmicro
®
Microcontroller Oscillator
Overview, Design Tips and
Troubleshooting of the PICmicro
®
Microcontroller Oscillator
In this presentation, we will explore the different oscillators and modes available on
PICmicro
®
microcontrollers (MCUs).
While oscillator design and usage is simple in concept, the selection of a wrong
oscillator for an application or oscillators that are not qualified properly can lead to
difficulties.
This presentation explores these issues and other so you will have a greater
understanding of oscillator design in general.
2
Getting Started - Oscillators
© 3.6.2001
Oscillator
Oscillator
Oscillator
l Covered Topics:
l PICmicro MCU Oscillator Modes
l Oscillator Design Tips
l Oscillator Qualification
l Troubleshooting Oscillators
l Covered Topics:
l PICmicro MCU Oscillator Modes
l Oscillator Design Tips
l Oscillator Qualification
l Troubleshooting Oscillators
Topics that will be covered include:
- PICmicro MCU Oscillator Modes -
Microchip Technology’s PIC
®
microcontroller is capable of supporting many
different oscillator types. The types supported depend on the device, and some are
more common than others. We will look at all modes that exist at the time this
presentation was created (December 2000)
- Oscillator Design Tips -
Next we will explore each of the different oscillators and how best to use them. Tips
will be broken down to suit each type of oscillator. The pros and cons of each will
also be described.
- Oscillator Qualification -
Then we will consider the conditions that are difficult on oscillators and how best to
deal with them. It happens that creating these conditions in the lab is an excellent
way to help qualify the oscillator component of your design.
- Troubleshooting Oscillators -
Finally, we will explore some of the more common mistakes in oscillator design and
testing. At the end of this section you will find a listing for more resources on
oscillators.
And now...
3
Getting Started - Oscillators
© 3.6.2001
Oscillator Mode Overview
Oscillator Mode Overview
Oscillator Mode Overview
Learning the types of oscillators
available for the PICmicro MCU
Learning the types of oscillators
available for the PICmicro MCU
... an overview of PICmicro Oscillator Modes.
First, we will look at the most commonly available oscillator modes.
4
Getting Started - Oscillators
© 3.6.2001
Oscillator - Mode Overview
Oscillator
Oscillator
-
-
Mode Overview
Mode Overview
l Modes and frequency ranges
l HS, XT, LP and RC are the most commonly
available oscillator modes
l Modes and frequency ranges
l HS, XT, LP and RC are the most commonly
available oscillator modes
There are 4 common oscillator modes that are available on most PICmicro devices.
HS, XT, LP and RC.
These modes support crystals, canned oscillator modules, some resonators or the use
of an external resistor and capacitor as a clock source. When using a crystal or
resonator, other components such as capacitors may be needed. We will look at this
later.
5
Getting Started - Oscillators
© 3.6.2001
Oscillator - Mode Overview
Oscillator
Oscillator
-
-
Mode Overview
Mode Overview
l HS High Speed
l Provides highest drive level available for
crystals and ceramic resonators
l Designed for 4 MHz and higher frequency
crystals and and most ceramic resonators
l Highest current consumption, but the fastest
mode available
l Popular mode for resonators since they tend to
require a stronger drive than crystals
l HS High Speed
l Provides highest drive level available for
crystals and ceramic resonators
l Designed for 4 MHz and higher frequency
crystals and and most ceramic resonators
l Highest current consumption, but the fastest
mode available
l Popular mode for resonators since they tend to
require a stronger drive than crystals
The HS mode stands for “High Speed” mode. It is designed to be used with crystals
and resonators with a frequency of 3 to 4 MHz or more. However, this is only a
guideline. The important thing to remember about HS mode is that it provides the
highest drive level available.
Crystals and Resonators must be DRIVEN by a signal to work. The gain on this
signal controls whether an oscillation will occur and how strong it will be. Care
must be taken not to underdrive or overdrive the crystal or resonator.
If there is too much drive, crystals suffer long-term damage, often failing in a matter
of weeks. With too little drive, the product may not start up correctly or may fail
under certain conditions. If these are problems you have encountered, be sure to see
the following sections and try modifying your drive level.
As a general rule, most resonators require more drive than crystals, so you will find
that HS mode is commonly used for resonators.
Two additional tips: Be sure to qualify your design to insure it is stable and does not
damage components. And remember, that as the frequency increases, the drive level
required tends to increase. This is why HS mode is designed for use with resonators
and crystals of 3 to 4MHz and faster.