The Basics of Programming and Using a
PIC Microcontroller
Authored By: Doug Bowlus
[db283101@ohio.edu]
The
purpose of this guide is to help those who are familiar with electronics and
writing PIC microcontroller software to program and use PIC microcontrollers at
home. The first part of this guide will
help select a PIC programmer by comparing the current options versus cost and
functionality. The second part of this
guide will demonstrate the use of one of the programmers mentioned in part I. The third and
final part will explain the setup and use of various supporting hardware
necessary to use the PIC microcontroller.
Part I: Selecting a Programmer
What programmer you will buy depends largely on how much
you want to spend and how much technical support you will need. The table below shows the various options I
looked at before making my decision.
|
Name |
Manufacturer |
Where to buy |
Comments |
Price (USD) |
|
Picstart Plus |
Expensive, serial, supports a large range of PICs, should
have good technical support |
$199 |
||
|
MPLAB ICD2 |
Expensive, usb, works with MPLAB to help debug programs
(will require two pins), should have good support. Price includes $40 Universal
Programming Module |
$228 |
||
|
Kit 149, USB / |
Cheap, serial/usb, programs a wide range of PICs, must be
soldered (it’s a kit), free programming software, limited technical
support. Price includes the fact that a 18Vdc wall wart and serial/usb cable must also be
purchased. ZIF socket is recommended, add about $10 |
$45 |
||
|
PICALL PIC Programmer |
Relatively cheap, parallel port computer connection, can
be bought as a kit or pre-assembled, supports a wide range of PICs and also
some other devices, software registration included, limited technical
support, Price includes 18Vdc wall wart and parallel cable. ZIF socket is recommended, add about $10 |
$85 |
||
|
K128 - USB all
Flash PIC Programmer |
Cheap, usb connection, no power supply required… runs off
usb power, programs a wide variety of PICs, free software, includes ZIF
socket, limited technical support, requires 9 components to be soldered.
Ozitronics is located in |
$65 |
||
|
WARP-13 |
A bit pricey, serial, programs most PICs and a couple
other devices, free software, compatible with the PICSTART PLUS (works with
MPLAB), comes with ZIF socket. May or
may not come with power supply and cables depending on distributor. |
$100 |
This
is by no means a complete list of all the PIC programmers out there; this is simply
a list of those that I feel are worth mentioning. Feel free to browse the manufacturer’s sites
to learn more about the programmers to help aid your decision.
I personally have had experience with the
PIC16PRO (not mentioned because it would be worth paying slightly more to get
the PICALL). I had no problems with this
programmer for a while and then after reformatting my computer, it began to not
work with my computer. I tested it on an
older system (found easily at state universities nowadays) and the programmer
worked fine. This means that the problem
I was having was software related but instead of spending more time trying to
find the problem, I decided to upgrade to a serial programmer.
The
second programmer I ended up buying was the Kit 149, USB / Serial Port PIC
Programmer. I have used this programmer
through both the serial port and the usb port and both worked just as
well. I have only had minor problems
with this device but this was because I bought it when the software was first
being developed. I was able to fix my
problems by using a different version of the software. Kitsrus has now released KIT149B which should
eliminate any issues I had.
In
the near future I would like to buy the K128
- USB all Flash PIC Programmer. This programmer eliminates the need for a
power supply and looks “more professional”.
It also uses the same software as the KIT149 which I will demonstrate in
Part II of this guide.
I have not personally used any of Microchip’s
programmers or the WARP-13 programmer, however I know people that own them and
have heard good things. These
programmers have the added bonus of working with MPLAB so you don’t have to
open up a separate program to program your PIC.
This may or may not be worth the money for you.
Part II: Programming a PIC with the KIT149 USB/Serial
Port Programmer
Although this section is specific to
the KIT149 programmer, the overall process should be similar for all the
programmers mentioned above. Before you
program your PIC, you should have already compiled your software in MPLAB
creating a file that has the same name as your assembly code file but ends in
“.hex”. This hex file contains the
machine code that will be programmed into your PIC.
1) With
the KIT149 powered and connected to your computer, open up its software,
Micropro. [Note: With the Microchip
programmers and WARP-13 there will be no need to open a separate software
program to program your PIC; Instead you should do
this in MPLAB.] You should now see something similar to this:
If
your com port settings are correct, “Board connected” will be displayed as in
the screenshot.
2) Select the type of
PIC you are using from the drop-down box (lower-right hand corner of the
screenshot). In this example, I am using
a PIC16F877. After doing this, a picture
of the PIC will be displayed sitting in a ZIF socket above the drop-down
box. Place your PIC in the programmer
(hopefully you purchased a ZIF socket to make removal easy) exactly like the picture. The 16F877 chip is 40 pins so all you have to
worry about is installing it in the correct direction, however with some of the
smaller chips, you must place them with pin1 in pin2 of the ZIF socket.
3) From the file menu select Load (or click the
LOAD button). It will now ask you for the
location of your hex file. Locate the
hex file you compiled in MPLAB and select Open.
The contents of your loaded hex file will now be displayed in the “ROM
DATA” window.
4) Now the fuses must be programmed if this has
not been done in your assembly file. To
program the fuses, click the Fuses button.
You should now see something similar to this:
Use
the drop-down boxes beside each fuse to set the desired values. The types of fuses available will change
depending on which PIC you are using, so if you unsure of what a fuse does,
check with the datasheet.
To eliminate the need to reselect the
correct fuses every time you re-program your PIC, you can specify them in your
assembly file. This is done with the __CONFIG
directive. [Note: The __CONFIG
directive requires that you must first use the LIST or PROCESSOR directive in
your assembly code to declare the type of PIC you are using.] A nice explanation of the __CONFIG directive
can be found in a Microchip document located at: http://www.microchip.com/download/lit/suppdoc/toots/config.pdf
An
example of using the __CONFIG directive is:
__CONFIG
_CP_OFF&_WDT_OFF&_BODEN_OFF&_PWRTE_ON
This
line will disable code protection, turn off the watchdog timer, turn off the
brown out detect and turn the power up timer on.
5) Now that you have loaded your hex file and
set your fuses, it is time to hit the program button. This will clear the PIC of its previous code
if it is not blank and then fill the PIC’s ROM with your new code. At this point you can use the Verify button
to ensure your code was properly programmed and then remove the PIC from the
ZIF socket and use it in your circuit.
Part III: Using a PIC Microcontroller Without a Demo Board
If you’ve taken microcontroller
classes at a university, chances are, you used a demo board. Using a demo board helps you concentrate on
learning to program software for the microcontrollers, but ultimately this makes
you unaware of the supporting hardware required. The supporting hardware for a PIC is very
minimal but without it, your microcontroller will not run.
For most PICs there are three main
things the PIC needs to run. The first
of these is power. You should connect
the appropriate positive voltage (typically 5 volts) to the Vdd pin and then
connect ground to Vss.
The second thing the PIC needs is an
oscillator. Depending on the PIC, you
have different options for the type of oscillator you can use; I will show how
to hook up a TTL crystal oscillator. You
will note in the schematic to the right that pins 7 and 14 are hooked to ground
and positive 5 volts respectfully. Pin 8
is then connected to the OSC1 pin on the PIC.
The reset circuit is the last thing that should be
built. If there is no need to have a
reset button, simply pull the MCLR_bar pin of the PIC high with a pull-up
resistor. To add a reset switch, keep
the pull-up resistor and add a switch connected to ground as shown in the
schematic.
Helpful Resources:
Microchip’s Website (http://www.microchip.com)
– Datasheets, Application Notes, Samples
Easy
Microcontrol'n A
Beginner's Guide to Using the PIC Microcontroller, by David Benson
Microcontrol'n Apps, PIC
Microcontroller Applications Guide by David Benson
Digi-key – Electronics
supplier
*Any questions or comments,
contact me: [db283101@ohio.edu]
© Doug Bowlus