what is the boot loader,
why we need it??
what is its purpose ???

 

It is a small program that is used to load larger programs. We need it because it would require removing the device an putting it in a programmer. The purpose is to get a program into a processor.

 

am using ICSP,
i didnt load it. but i can program my chip 18f452 with different HEX file.

 

am using ICSP,
i didnt load it. but i can program my chip 18f452 with different HEX file.

A bootloader allows you to do the same thing without any hardware assist like ICSP, usually through a standard serial port. Maybe most PICs do not support such a thing, but the Atmel chips certainly do.

 

am using ICSP,
i didnt load it. but i can program my chip 18f452 with different HEX file.

Through the ICSP you are loading the HEX file with a programmer; for which you don't need a bootloader.

But what if you didn't have a programmer, and need to load a HEX file directly with a USB cable connected to the PIC?... that would require a bootloader; which is a program that loads and executes your programs instead of doing it directly.

For example: you don't need a programer to load a sketch into an arduino; that's because its bootloader does it through the serial coms by the USB cable.

 

A bootloader allows you to do the same thing without any hardware assist like ICSP, usually through a standard serial port. Maybe most PICs do not support such a thing, but the Atmel chips certainly do.

You can do it with a PIC that has a USB peripheral. both the MCHPFSUSB and MLA come with bootloaders.

 

At the dawn of computer time we had to key in a boot loader with toggle switches, and then execute it, to read the OS off of paper tape or other input devices. We sure do have it lucky these days.

 

Also it helps to understand the origin of the term boot loader. It is the shorten form of bootstrap loader.

Hence check the origin of the term bootstrap and booting.

http://en.wikipedia.org/wiki/Bootstrapping

http://en.wikipedia.org/wiki/Booting

The first computers came with a blank memory, i.e. there was no coherent program in the program memory.
You had to manually enter the shortest possible program into the computer memory via front panel toggle switches.

After doing this a few dozen times one would memorize the code.

Here is the bootstap loader (Read-In-Mode) for the DEC PDP-8 minicomputer:

07756  6014  RCC
07757  6011  RSF
07760  5357  JMP .-1
07761  6016  RRB
07762  7106  CLL RTL
07763  7006  RTL
07764  7510  SPA
07765  5357  JMP 7757
07766  7006  RTL
07767  6011  RSF
07770  5367  JMP .-1
07771  6016  RRS
07772  7420  SNL
07773  3776  DCA I 7776
07774  3376  DCA 7776
07775  5356  JMP 7756
07776  0000  AND 0
07777  5301  JMP 7701

And here is the bootstrap loader for the Data General Nova 2 minicomputer:

17757 126440 GET: SUBO 1,1
17760 063610     SKPDN TTI
17761 000777     JMP .-1
17762 060510     DIAS 0,TTI
17763 127100     ADDL 1,1
17764 127100     ADDL 1,1
17765 107003     ADD 0,1,SNC
17766 000772    JMP GET+1
17767 001400    JMP 0,3
17770 060110 BSTRP:   NIOS TTI
17771 004766     JSR GET
17772 044402    STA 1,.+2
17773 004764    JSR GET

You only had to memorize the middle column of numbers.

 

At the dawn of computer time we had to key in a boot loader with toggle switches, and then execute it, to read the OS off of paper tape or other input devices. We sure do have it lucky these days.

It can't be any other way, when a simple 1 dollar MCU has 10 times more memory and is 20 times faster than my first computer.

 

Remember this piece of doggerel?

ACHTUNG!
ALLES TURISTEN UND NONTEKNISCHEN LOOKENPEEPERS!
DAS KOMPUTERMASCHINE IST NICHT FÜR DER GEFINGERPOKEN UND MITTENGRABEN! ODERWISE IST EASY TO SCHNAPPEN DER SPRINGENWERK, BLOWENFUSEN UND POPPENCORKEN MIT SPITZENSPARKEN.
IST NICHT FÜR GEWERKEN BEI DUMMKOPFEN. DER RUBBERNECKEN SIGHTSEEREN KEEPEN DAS COTTONPICKEN HÄNDER IN DAS POCKETS MUSS.
ZO RELAXEN UND WATSCHEN DER BLINKENLICHTEN.

 

If I recall correctly, that was manditory posting on every minicomputer with flashing lights.

 

If I recall correctly, that was manditory posting on every minicomputer with flashing lights.

I first saw it on the console of the Princeton University IBM 7090 in 1962

 

Never saw that before. Still laughing

 

I first saw it on the console of the Princeton University IBM 7090 in 1962

I saw it at MIT on an IBM 1130! Ca 1968