8-bit microcontrollers

[samcheetah]

from what i know all PICs, AVRs and 8051 derivatives are 8-bit microcontrollers. right??? but then the Microchip Midrange reference manual states that PICs are grouped by the size of their instruction word which are Base Line---12-bit instruction word, Midrange---14-bit instruction word, High End---16-bit instruction word. now what does that mean? should 8-bit microcontrollers have 8-bit instruction words?

i remember the term "instruction word" in the VLIW (very long instruction word) does this have something to do with that.

i remember that i read somewhere that there are CISC processors with a complex instruction set and then there are RISC processors with a reduced instruction set and then there are VLIW processors which have very long instruction words.

so are PICs actually VLIW based microcontrollers or am i just babbling about things i dont know :lol:

 

[Nigel Goodwin]

from what i know all PICs, AVRs and 8051 derivatives are 8-bit microcontrollers. right??? but then the Microchip Midrange reference manual states that PICs are grouped by the size of their instruction word which are Base Line---12-bit instruction word, Midrange---14-bit instruction word, High End---16-bit instruction word. now what does that mean? should 8-bit microcontrollers have 8-bit instruction words?

i remember the term "instruction word" in the VLIW (very long instruction word) does this have something to do with that.

i remember that i read somewhere that there are CISC processors with a complex instruction set and then there are RISC processors with a reduced instruction set and then there are VLIW processors which have very long instruction words.

so are PICs actually VLIW based microcontrollers or am i just babbling about things i dont know :lol:

Yes you are 8)

A PIC is an 8 bit RISC processor, regardless of it's instruction word length. The bit size of a processor refers to how large a piece of memory it handles, which in the PIC's case is always 8 bits. The full instruction words are longer than this due to the Harvard architecture used, where both the instruction and the data are included in the same longer instruction word.

This is only possible because of the small number of instruction words in the RISC processor, with a 16 bit long word you can have 8 bit data and up to 256 actual instructions (8 bits). With a 14 bit word you can have 8 bit data and up to 64 instructions (6 bits), and with a 12 bit word you can have 8 bit data and only 16 instructions (4 bits).

This isn't quite true (but the basic principle is), a number of instructions don't require an 8 bit data byte, for example 'BCF PortA, 1' where the data byte is only 3 bits (0-7) - this allows the 12 bit core PIC's to have more than the suggested 16 instructions.

To confuse things even further, the high end 16 bit core PIC's have some instructions which take more than one instruction word - unlike the 12 and 14 bit core, where all instructions fit in a single word.

I hope this clears things up for you?.

 

[samcheetah]

yes it sure did. but if i hadnt read a little about microprocessors and microcontrollers that would have been greek to me :lol:

can u refer me to some article or book in which i could further understand the architechture of PICs and microcontrollers in general.

man u should manage a little bit of time and start writing a book!!!!!!

 

[Divs]

i couldnt agree more..
Nigels way of explaining stuff is too good

 

[Sceadwian]

There are dozens and dozens of books out there, and more online information than you could possibly view in a lifetime. Wikipedia has a large amount of information relativly well cross-refrenced. Look up their entries on PIC microcontroller and AVR (AVR's are similar to PIC's only produced by a company called Atmel) When your eyes start glazing over while you're reading STOP and find out what's confusing you and look that up.

I've spent my spare time on web sites and Wikipedia for the last few years learning about micro controllers, electricity, and electronics and I'm just barelly starting to get into the hard stuff (semi-conductor theory and operation) There are entire fields within sub catagories of electronics that I'll never even know about.

 

[Oznog]

PICs are no longer all 8 bit.
dsPIC30F, dsPIC33F, and PIC24 series are 16 bit cores. All operations work in byte or word mode. Some even have a double word (32 bit) mode.
The Working Registers are 16 bits wide, and there are also 2 40-bit Accumulators (another type of Working Register which works with a different set of instructions).
The instruction words are 24 bits long. This is sort of tough on program memory useage except that dsPIC's instructions are very effective and the number of required instructions is often much lower.

 

[Nigel Goodwin]

PICs are no longer all 8 bit.

A lot changes in two years!.

 

[Sceadwian]

Oznog, those aren't really pics anymore. All AVR's aren't 8 bit anymore either, they have an AVR32 series which is basically a next generation ARM architecture with a DSP slant. AVR32's are NOT AVR's. PICDSP's or whatever you'd like to call them are NOT pics. The AVR32 and the PICDSP series of chips both break that line from micro controller to programmable DSP.

 

[hjames]

VLIW is a specific term given to processors which can execute many instructions in a single clock cycle and are designed in conjunction with a relatively "smart" compiler. Some high-end DSP's are VLIW types, but they're pretty rare.

 

[KIMBERWICK]

Try looking up the arduino uno on google. THERE IS A TON OF WEB SITES ABOUT THIS POWERFULL BOARD FOR BEGINNER OR EXPERT EITHER SOFTWARE OR ELECTRONICS

 

[be80be]

AVR32 are really AVR 32 I think it looks more like AVR is letting Arm use there ideas and in turn there using peripheral controllers and bus ideas that are Arm.

So it's a AVR32 UC3 core with peripheral controllers and bus designs first seen in the AT91SAM ARM-based platforms

I don't care what it is I like them ARM or AVR there sweet.

 

[lurkepus]

I'm new to electronics and mcu's and i have found the best way (for me atleast) is to use one manufacturer and the info found about their mcu's just to get the hang of things .. I startet of with the microchip mcu's and haev been reading alot about their products :They have a big liberary of info and datasheets withc have helped me a lot try https://www.microchip.com/ and see if you can get the info needed on their website