- Starting
your PIC Engine
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- Start Line - Before You
Write Your First Code of PIC 16F877
- Now you're in the class and gotta be ready
for a small or big project using PIC16F877. Lecture notes
are everywhere and some example codes you attained and
stashed inside your USB memory stick. Before you take
that code out from the stick, you have to stand, and
get-set, at the start line. I mean that you have to have
a minimum hardware for PIC16F877 application. The minimum
hardware configuration, which you can build from scratch
either on your breadboard or project board, can be found
in Chapter 4 of my book, Embedded
Computing with PIC16F877-Assembly Language Approach.
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- PIC16F877 and
PIC16F887A
- In the configuration, you need a PIC16F877
or PIC16F877A. The 16F877A is a brother (I would say a
twin brother, delivered much later though than its elder
brother) of 16F877. I noticed that 16F877A is slightly
cheaper and, so far, I found only one difference in the
pin assignment. That's very minor. I used to use 16F877
chips only, of course. Since late last year, I see only
16F877A from the students who visit my office for
bootloader download to the chip. Whether you choose
16F877 or 877A, I recommend you choose the chip properly
according to my guideline: package type must be DIP
(Dual-in line) so that it goes through the holes in your
breadboard or project board, and the clock speed of 20MHz
(Even though PIC16F877/877A supports 4 or 8 MHz also, but
do we not utilize the maximum speed the chip promises,
20MHz. I always use 20MHz speed, and all the source codes
in my book are based on 20MHZ clocking.
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- MAX232
- The only other chip you need is MAX232,
RS-232 level converter. RS-232 is a regulation for the
voltage level for binary numbers. Something like -15V for
"1" and 20V for "0". Sorry I do not
remember the exact value of the voltage levels for the
binary values. But the message is clear. In RS-232 rule,
binary expression is done in two very different levels of
voltage. Long time ago, data transmission is done by
something called tele-type, signal attenuation over the
long distance is significant. At least that's what they
say. So increasing the voltage level would increase the
performance of the communication. Even though we're in
all digital age, somehow we still use RS-232 regulation.
In desktop PCs, most notably. At the back of your PC,
find a 9-pin connector designated for serial
communication port. Out of the pins are the voltage
levels determined by binary values. In other words,
everything inside your PC is done digitally (1/0 logic or
+5V/0V logic). When a byte of data comes out of your PC
through the DB-9 connector, they are converted to the
RS-232 logic. Therefore, MAX232 (or any equivalent 232
chip) is to covert binary logic system to RS-232 logic
system. Now you rightly guess why we need a MAX232 chip.
It is to convert the digital logic in 16F877 to RS-232
level, so that this RS-232 logic can be transmitted via
RS-232 logic DB-9 connector to your PC. Or a byte data
from PC in digital logic is converted to RS-232 logic via
MAX232 (or equivalent chip) inside PC is entered in to
your PIC board, first through your MAX232 chip, reversed
to digital logic, then to your 16F877 in binary logic. In
MAX232 chip, you will need four 1-micro Farad electrolyte
capacitors. See Chapter 4 of my book, Embedded
Computing with PIC16F877-Assembly Language Approach.
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- Laptop without DB-9 but
with USB only
- Nowadays, manufacturers of laptop PC do
not bother to include DB-9 connectors. Instead they
install only USB slots. This will give you pain when you
have MAX-232 and DB-9 male/female connector ready for
DB-9 connector in your laptop. One option is to buy a
Serial-to-USB converter. This thing has two types of
connectors. DB-9 at one end and USB at the other end.
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- PIC USB Board
- Or you can buy a PIC board from Olimex
(www.olimex.com) which has everything including USB
connector. This board comes with PIC16F877A. Or if they
changed their product or policy, you may have to buy a
16F877A chip along with the board. The board must be a
40-pin board, with built-in 20MHz crystal and all the
necessary accessories. The olimex board with USB is the
product number PIC-40B-USB. The PIC board from Olimex
with DB-9 connector with power supplying circuit is
PIC-40B. The PIC-40B-USB does not have power supply
circuit since USB connection can draw power from your PC
or laptop. When you purchase PIC-USB-40B, you have to install
a USB serial communication driver and you need to know
how to find the COM port number of your USB-ed PIC board to your PC.
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- Bootloader for
PIC16F877 and 877A
- Once you have your PIC board with
PIC16F877 or 16F877A, you have to have a bootloader
burned into your PIC chip. A bootloader is a small size
code which opens up communication between the PIC chip
and host PC (your desktop PC or your laptop) via a serial
communication program, most notably HyperTerminal in
Windows operating system, or a specific PIC downloader
(available here or try this
website). What bootloader does
is to allow you to download your hex code (assembled
using any PIC assembler, for example, MPLAB or MPASM)
inside the PIC chip and burn the flash memory of the PIC
chip. Once you burn your bootloader (itself a hex code)
in the flash memory of your PIC chip, you're now free
from any hassle. You just connect your USB or serial
communication to your PC or laptop, and use the PIC
downloader to download your hex code. The bootloader
remains unchanged no matter what. OK. Now where can you
find the bootloader for PIC 16F877 and 16F877A? Of course
free ones. The best place I know is the microchip web
site. Go visit http://www.microchipc.com/PIC16bootload/ and select the following http://www.microchipc.com/PIC16bootload/PIC16F87xA_bootloader_v9-30.zip link and down load. Inside this zip file you
will see many different versions of bootloader. 16F87x
4MHz 19200bps, 16F87xA 20MHz 56000bps etc. Source codes
and hex codes altogether. Somebody did a real good job.
Anyway, the first one is apparently the chip, and the
second tells you your crystal speed, and the third one is
the serial communication bps (bit per second). This bps
must be the same as the bps you will select in the PIC
downloader. OK. I think now you have (1) the necessary
bootloader hex code and (2) PIC downloader.
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- PIC Burner (or PIC
programmer)
- A PIC burner is a physical PIC programmer.
A "physical: programmer is not a person who is a
programmer. A physical programmer is a small board which
burns your bootloader hex code into you PIC chip so that,
later, you can download your own code to your PIC chip
using the PIC downloader. There are many types of PIC
burners with different functions and of course price
tags. The one I use is very simple and cheap. It's from
Olimex and the product number is PIC-PG2C. This slick
board with 40-pin IC socket does not need external power
supply. All you need is a serial cable. And the burn
software is available from the Olimex web site and its
name is ICPROG.EXE. The speed selection in ICprog window
must be HS (high speed) since we use the maximum
oscillation of 20MHZ. Other selections you can leave as
default.
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- Finally
- Now you have everything. PIC board with
PIC chip. PIC Downloader. PIC Burner. PIC bootloader. The
source codes I developed originally for PIC16F877
perfectly works with PIC16F877A. In your code section at
the first line, you don't even have to declare as
16F877A. You can leave as it is with PIC16F877. But in
your PIC burner, you have to select PIC16F877A and
corresponding bootloader. Now ladies and gentlemen, start
your engine!
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- You need help?
- If you meet any problem in the start line,
after a long search and tries, please write to me at ckimson@gmail.com
- Return to PIC Book Page
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