Hi,
How
are you doing? Hope everyone is fine… Today I am going to start on the
introduction of the most important component in my Final Year Project (FYP),
which is the microcontroller. I am using a PIC16F887A by Microchip.
So
let’s learn more about PIC microcontrollers.
Introduction
A
PIC microcontroller is a processor with built in memory and RAM, and you can
use it to control your projects. So it saves you building a circuit that
has separate external RAM, ROM and peripheral chips. It is a very powerful
device that has many useful built in modules. For example:
- EEPROM
- Timers
- Analogue comparators
- UART
The
PIC 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. Click here for the PIC16F877A datasheet
Features
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 and etc.
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. PIC12F675 not PIC12C509). 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. That’s so cool right…hehe
You
can either program a PIC microcontroller using assembler or a high level
language. I recommend using a high level language such as C as it is much
easier to use.
Input /
Output (I/O)
A
PIC Microcontroller can control outputs and react to inputs. For example,
you could drive a relay at the output or read input buttons. Many
now have a built in ADC so you can read analogue signal levels so you don't
need to add an external device.
Peripherals
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…..hehe <3
PIC microcontroller
Feature |
PIC microcontroller
feature description |
Flash memory
|
Re-programmable program
storage.
|
Memory storage for
variables.
|
|
Long term stable memory: Electrically
Erasable Programmable Read Only Memory.
|
|
High current Input/Output
ports (with pin direction change).
|
|
Typically 3.
|
|
Built in RS232 protocol
(only needs level translator chip).
|
|
Capture/Compare/PWM
module.
|
|
I2C and SPI Interfaces.
|
|
An analogue comparator
and internal voltage reference.
|
|
Analogue to digital
converter.
|
|
Parallel Slave Port (for
8 bit microprocessor systems).
|
|
LCD interface.
|
|
ICSP,WDT,BOR,POR,PWRT,OST,SLEEP
|
|
Simple programming using
In Circuit Serial Programming.
|
Note:
these are some of the main features (some chips have all of these and some
don't).
Flash memory
This
is the program storage area and gives you the most important benefit for
using a PIC microcontroller. It allows you to program the device many times. It
can be re-programmed up to 100,000 times (probably more) as they use
Flash memory
ICSP
In
Circuit Serial Programming (ICSP)
is the next most important benefit. 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. J
I/O Ports
Input
/ Output ports let you communicate with the outside world so you can
control leds, LCDs or just about anything with the right interface. You
can also set them as inputs to gather information.
Pin direction
Most
PIC microcontroller pins can be set as an input or an output. This allows you
to use a pin for multiple operations. For example, the Real Time clock project uses RA0, the first pin
of PORTA, to output data to a seven segment display and at a later point in the
program read the analogue value as an input.
Current
The
PIC I/O ports are high current ports capable of directly driving LEDs (up to
25ma output current) - the total current allowed usually ~200mA this is often
for the whole chip.
Timer / Counters
Each
PIC microcontroller has up to three timers that you can either use as a
timer or a counter (Timer 1 & 2) or a baud clock (Timer 2).
USART
The
USART is a useful module and saves having to code up a software version so it
saves valuable program memory. All you need to interface it to a PC serial port
is a MAX232 chip (or equivalent).
Baud Rates
You
have to be careful using the baud rates as they depend on the main clock in use
and normal oscillator values in general do not fit very well with 'real' baud
rates.
CCP
The
Capture/Compare/PWM module has three modes of operation:
- Capture - Capture the time of an event.
- Compare - Generate an output when Timer 1 reaches a value.
- PWM - Pulse Width Modulation.
Comparator and comparator voltage reference
The
comparator is module that has two analogue comparators which can be set up in
one of 8 different ways. Either digital or analogue inputs can be compared to
reference voltages.
In
one mode an internally generated voltage reference is used as an input to both
comparators and in the same mode multiplexing lets you monitor up to four
different input pins.
ADC
The
single 10 bit Analogue to Digital Converter can have up to 8 inputs for a
device multiplexed from input pins.
The
ADC can be used during sleep but you have to use the RC clock mode. One benefit
of this is that there will be no digital switching noise so you will get better
conversion accuracy.
PSP
The
Parallel Slave Port lets you to connect the PIC microcontroller directly into a
microprocessor system. It provides an 8 bit read/write data bus and RD (read)
WR (write) and CS (chip select) inputs - all active low.
This
will let you add a PIC microcontroller to a system so that the PIC
microcontroller can be treated as a memory mapped peripheral. It will let
the microcontroller behave just as though it was another microprocessor
building block e.g. some memory or ram but in this case you have full control
over exactly what the building block is i.e. you can re-program the PIC
microcontroller to do just about anything..
Special Features
ICSP
|
In
Circuit Serial Programming
|
Refer ICSP
above
|
WDT
|
Watch dog timer
|
This is a software error
protector.
|
BOR
|
Brown Out reset
|
This detects if the power supply
dips slightly and resets the device if so.
|
POR
|
Power on reset
|
This starts
microcontroller initialization.
|
PWRT
|
PoWeR up Time
|
A time delay to let Vdd rise.
|
OST
|
Oscillator start up timer
|
Wait for 1024 cycles after PWRT.
|
SLEEP
|
PIC microcontroller sleep mode
|
Enter low power mode.
|
All
three devices are extremely powerful and the main difference is that they have
different numbers of pins and memory size.
PIC microcontroller
Device
|
PIC microcontroller No.
Pins
|
PIC microcontroller Flash
memory WORDS
|
PIC12F675
|
8
|
1k
|
PIC16F88
|
18
|
4k
|
PIC16F877A
|
40
|
8k
|
(Note: that all of them have the letter F in - this means it is a Flash re-programmable part - don't go and buy a part with O in as its OTP - programmable only once!)
So, that's it for now I guess... Next I will discuss on the PIC main board PCB designing and its etching procedures. Hope you enjoy this entry. Tata for now....! :)
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QUOTE of the day...!!!
Life is like riding a bicycle - in order to keep your balance, you must keep moving. ~Albert Einstein
Regards,
Idriah Safriza :)
