What is a PICmicro?

The PICmicro was originally designed around 1980 by General Instrument as a small, fast, inexpensive embedded microcontroller with strong I/O capabilities. PIC stands for "Peripheral Interface Controller". General Instrument recognized the potential for the little PIC and eventually spun off Microchip, headquartered in Chandler, AZ to fabricate and market the PICmicro.

The PICmicro has some advantages in many applications over the older chips such as the Intel 8048/8051/8052 and its derivatives, the Motorola MC6805/6hHC11, and many others. Its unusual architecture is ideally suited for embedded control. Nearly all instructions execute in the same number of clock cycles, which makes timing control much easier. The PICmicro is a RISC (Reduced Instruction Set Computer) design, with only thirty-odd instructions to remember; its code is extremely efficient, allowing the PIC to run with typically less program memory than its larger competitors.

Very important, though, is the low cost, high available clock speeds, small size, and incredible ease of use of the tiny PIC. For timing-insensitive designs, the oscillator can consist of a cheap RC network. Clock speeds can range from low speed to 20MHz. Versions of the various PICmicro families are available that are equipped with various combinations ROM, EPROM, OTP (One-Time Programmable) EPROM, EEPROM, and FLASH program and data memory. An 18-pin PICmicro typically devotes 13 of those pins to I/O, giving the designer two full 8-bit I/O ports and an interrupt. In many cases, designing with a PICmicro is much simpler and more efficient than using an older, larger embedded microprocessor.

SOURCE FROM: botkin.org

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PIC Microcontroller Introduction

A PIC microcontroller is a processor with built in memory and RAM and you can use it to control your projects (or build projects around it). So it saves you building a circuit that has separate external RAM, ROM and peripheral chips.

What this really means for you is that you have a very powerful device that has many useful built in modules e.g.

* EEPROM.
* Timers.
* Analogue comparators.
* UART.


Even with just these four modules (note these are just example modules - there are more) you can make up many projects e.g.:

* Frequency counter - using the internal timers and reporting through UART (RS232) or output to LCD.

* Capacitance meter - analogue comparator oscillator.

* Event timer - using internal timers.

* Event data logger -capturing analogue data using an internal ADC and using the internal EEPROM for storing data (using an external I2C for high data storage capacity.

* Servo controller (Control through UART) - using the internal PWM module or using a software created PWM.

The PIC Micro is one of the most popular microcontrollers and in case you were wondering the difference between a microprocessor and a microcontroller is that a microcontroller has an internal bus with in built memory and peripherals.

In fact the 8 pin (DIL) version of the 12F675 has an amazing number of internal peripherals. These are:

* Two timers.
* One 10bit ADC with 4 selectable inputs.
* An internal oscillator (or you can use an external crystal).
* An analogue comparator.
* 1024 words of program memory.
* 64 Bytes of RAM.
* 128 Bytes of EEPROM memory.
* External interrupt (as well as interrupts from internal peripherals).
* External crystal can go up to 20MHz.
* ICSP : PIC standard programming interface.

And all of these work from within an 8 pin DIL package!

In the mid-range devices the memory space ranges from 1k to 8k (18F parts have more) - this does not sound like a lot but the processor has an efficient instruction set and you can make useful projects even with 1k e.g. LM35 temperature sensing project that reports data to the serial port easily fits within 1k.

Features
In fact a PIC microcontroller is an amazingly powerful fully featured processor with internal RAM, EEROM FLASH memory and peripherals. One of the smallest ones occupies the space of a 555 timer but has a 10bit ADC, 1k of memory, 2 timers, high current I/O ports a comparator a watch dog timer... I could go on as there is more!
Programming
One of the most useful features of a PIC microcontroller is that you can re-program them as they use flash memory (if you choose a part with an F in the part number e.g. 12F675 not 12C509). You can also use the ICSP serial interface built into each PIC Microcontroller for programming and even do programming while it's still plugged into the circuit!

You can either program a PIC microcontroller using assembler or a high level language and I recommend using a high level language such as C as it is much easier to use (after an initial learning curve). Once you have learned the high level language you are not forced to use the same processor e.g. you could go to an AVR or Dallas microcontroller and still use the same high level language.
Input / Output - I/O
A PIC Microcontroller can control outputs and react to inputs e.g. you could drive a relay or read input buttons.

With the larger devices it's possible to drive LCDs or seven segment displays with very few control lines as all the work is done inside the PIC Micro.

Comparing a frequency counter to discrete web designs you'll find two or three chips for the microcontroller design and ten or more for a discrete design. So using them saves prototype design effort as you can use built in peripherals to take care of lots of the circuit operation.

Many now have a built in ADC so you can read analogue signal levels so you don't need to add an external devices e.g. you can read an LM35 temperature sensor directly with no interface logic.
Peripherals
The PIC microcontroller has many built in peripherals and this can make using them quite daunting at first which is why I have made this introductory page with a summary of each major peripheral block.

At the end is a short summary of the main devices used in projects shown on this site.

The best way to start is to learn about the main features of a chip and then begin to use each peripheral in a project. I think learning by doing is the best way.
Flash memory
This is the program storage area and gives you the most important benefit for using a PIC microcontroller - You program the device many times. Since when does anyone get a program right first time ?

Devices used in projects on this site can be re-programmed up to 100,000 times (probably more) as they use Flash memory - these have the letter F in the part name. You can get cheaper (OTP) devices but these are One-Time-Programmable; once programmed you can't program it again!
ICSP
In Circuit Serial Programming (ICSP) is the next most important benefit. Instead of transferring your chip from the programmer to the development board you just leave it in the board. By arranging the programming connections to your circuit correctly you won't need to remove the chip!

You can re-program the device while it's still in the circuit so once your programmer is setup you can leave it on the bench and test your programs without moving the chip around and it makes the whole process much easier.

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Fuzzy Logic and Neural Networks

Fuzzy Logic and neural networks are two design methods that are
coming into favor in embedded systems. The two methods are very
different from each other, from conception to implementation.
However, the advantages and disadvantages of the two can complement
each other.

The advantage of neural networks is that it is possible to design
them without completely understanding the underlying logical rules by
which they operate. The neural network designer applies a set of
inputs to the network and "trains" it to produce the required output.
The inputs must represent the behavior of the system that is being
programmed, and the outputs should match the desired result within
some margin of error. If the network's output does not agree with
the desired result, the structure of the neural network is altered
until it does. After training it is assumed that the network will
also produce the desired output, or something close to it, when it
presented with new and unknown data.

In contrast, a fuzzy-logic system can be precisely described. Before
a fuzzy control system is designed, its desired logical operation
must be analyzed and translated into fuzzy-logic rules. This is the
step where neural networks technology can be helpful to the
fuzzy-logic designer. The designer can first train a software neural
network to produce the desired output from a given set of inputs and
outputs and then use a software tool to extract the underlying rules
from the neural network. The extracted rules are translated into
fuzzy-logic rules.

Fuzzy logic is not a complete design solution. It supplements rather
than replaces traditional event control and PID (proportional,
integral, and derivate) control techniques. Fuzzy logic relies on
grade of membership and artifical intelligence techniques. It works
best when it is applied to non-linear systems with many inputs that
cannot be easily expressed in either mathematical equations used for
PID control or IF-THEN statements used for event control.

In an effort to change fuzzy logic from a "buzzword" (as it is in
most parts of the world) to a well established design method (as it
is in Japan), most manufacturers of microcontrollers have introduced
fuzzy logic software. Most software generates code for specific
microcontrollers, while other generates C code which can be compiled
for any microcontroller.

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Interpreters

An interpreter is a high level language translator that is closer to
natural language. The interpreter itself is a program that sits
resident in the microcontroller. It executes a program by reading
each language statement one at a time and then doing what the
statement says to do. The two most popular interpreters for
microcontrollers are BASIC and FORTH.

BASIC's popularity is due to its simplicity, readability, and of
course just about everyone has at least played with BASIC at one time
or another. One common compaint about [interpreted] BASIC is that it
is slow. Often this can be solved by using a different technique for
performing the desired task. Other times it is just the price paid
for using an interpreter.

FORTH has a very loyal following due to its speed (approaching that
of assembler language) and its incremental approach to building a
system from reusable parts. Many FORTH systems come with a host
system which turns your desktop computer into a development system.
FORTH can be quite difficult to write in (if you have no experience
with it) and is probably even harder to read. However, it is a very
useful and productive language for control systems and robotics, and
can be mastered in time.

The nicest thing about developing a system with an interpreter is
that you can build your program interactively. You first write a
small piece of code and then you can try it out immediately to see
how it works. When the results are satisfactory, you can then add
additional components until the final product is achieved.

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Compilers

A compiler is a high level language translator that combines the
programming ease of an interpreter with greater speed. This is
accomplished by translating the program (on a host machine such as a
desktop PC) directly into machine language. The machine language
program is then burned onto an EPROM or downloaded directly to the
microcontroller. The microcontroller then executes the translated
program directly, without having to interpret first.

The most popular microcontroller compilers are C and BASIC. PL/M,
from Intel, also has some popular support due to that company's
extensive use of that language.

Due to both its popularity and its slow speed, it was only logical
that BASIC would appear as a compiled language. A few companies
supply a BASIC compiler for several of the more popular
microcontrollers. Execution speed is drastically increased over
interpreted BASIC since the microcontroller is freed from the task of
interpreting the statements as the program runs.

While interpreted Forth approaches (and sometimes surpasses) the
speed of many compilers, compiled Forth screams along. Today there
are many high performance optimizing native code Forth compilers, and
there are also lots of very cheap or free public domain Forths. Some
of them like Tom Almy's ForthCMP produces optimized native code with
less overhead and better performance than just about anything else
out there. Of course it still has compactness and more elegant
factoring of functionality than in most languages.

C is now the language of choice for the entire universe. C is used
on computers from the tiny microcontroller up to the largest Cray
supercomputer. Although a C program can be a bit tedious at times to
read (due to the terse programming style followed by many C
programmers), it is a powerful and flexible development tool.
Although a high level language, it also gives the developer access to
the underlying machine. There are several very good and cheap C
compilers available for the more popular microcontrollers. It is
widely used, available, supported, and produces fairly efficient code
(fast and compact).

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Assembly language

Machine language is the program representation as the microcontroller
understands it. It is not easy for humans to read and is a common
cause of migraine headaches. Assembly language is a human-readable
form of machine language which makes it much easier for us flesh and
bone types to deal with. Each assembly language statement
corresponds to one machine language statement (not counting macros).

An assembly/machine language program is fast and small. This is
because you are in complete charge of what goes into the program. Of
course, if you write a slow, large, stupid program, then it will run
slowly, be too big, and be stupid. Assembly language (assembler)
can't correct stupidity - although sometimes I wish it could ;-).

If you are starting out learning about microcontrollers, it would be
worth your while first learning assembler. By programming in
assembler, you master the underlying architecture of the chip, which
is important if you intend to do anything significant with your
microcontroller.

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