PIC Micro's For Beginners - How to wire
up a PIC
PIC micro's do not need much
to operate, just a steady and stable voltage for Vdd and MCLR, and
an external oscillator if you are not using the internal oscillator
on the PIC.
The diagram below explains how
to hook up the basic requirements of the
PIC micro, and although an
18 Pin PIC has been used in this example, the same analogy applies
to any
PIC micro, that is,
5 Volts too
MCLR
Vdd (40 pin PIC's have 2 Vdd's)
Earth (GND) to Vss (28 and 40 Pin
PIC's have 2 Vss)
A crystal oscillator with loading
capacitors if the internal oscillator is not used
When in doubt, consult the
PIC micro datasheet for the PIC you are using! Here's
an example of wiring up an 18 Pin PIC;
Internal Oscillator
Why use an external crystal
oscillator if most PIC's have one built in? Well its because the
internal oscillator is not nearly as accurate when compared to
crystal oscillators, and for timing crucial (within nS range)
applications this is important to know. Of course this is not
required for 95% of projects/applications, just something to
consider.
As most of my code examples
are written with
Swordfish, there is one important factor to consider with the
internal oscillator: the internal oscillator will
default too 31Khz, and when
Library Files are included for use within programs, they could
(will) have initialization
routines that will execute before your main program. This leads to
long "start up delays" as the
code to setup the internal oscillator is not actioned until the
program has "initialised". Solution: make a
User Library that initialises the internal oscillator clock
speed, and simply included it first. Have a look at the
PIC Transitions page I put together for different devices I use!
The capacitors
The 10uF electrolytic
capacitor is required to maintain a steady input voltage to the
regulator, and should be used in all designs. If you are driving
high current loads, then use a bigger capacitor, but in most cases,
10uF will be suffice. Keep in mind that electrolytic capacitors are
polarity sensitive, and the negative lead is marked with a band on
the side of the case.
The 0.1uF ceramic disc capacitor is used to
remove transient noises on the output. These are high
frequency noises/spikes created from a
range of sources and anomalies on your target circuit, and although
not required on non timing crucial applications, I still place one
to ensure the accurate timing operation of the PIC. Ceramic disc
capacitors are not polarity sensitive.
The 5 volt regulator (7805)
can have a much higher input voltage then 12 volts, but heat becomes
an issue even with small loads. More information about
how to build voltage regulator circuits can be found here.
Basics
Section: