AVR-Chat

Kong wrote:

>hi all,
>foa, newbie here, so pls go easy, if you could ;-)
>i'm looking at building a weather station. google tells me there are a 
>few out there based on PIC. someone suggested AVR atmega169 but i'm put 
>off by its mlf packaging.
>i'll need adc, lcd, push buttons, ram/flash to store data history, 
>serial to PC later. it looks like pic16f877 should be the trick for me 
>but i figure i should give avr a chance. so i'm here looking at the 
>whys/why-nots of using AVR to build my weather station.
>ok. flame away.
>cheers
>-ls kong
>  
>
Kong,

  There is nothing inherently "wrong" ( or "right," for that matter)in 
choosing a PIC over an AVR, or vice versa.  Among the denizens of this 
particular mailing list you will, of course, find most promoting and 
advocating the use of the AVR family (odd thing, that).

  My take on the ifferences is as follows (not necessarily in any order 
of importance):

1)  efficiency.  The PIC line is a four phase clocking architecture, 
which means that each instructiins take at LEAST 4 clock cycles to 
complete.  The AVR is a single-phase clocling architecture.  The 
majority of instructions cvomplete in a single clock cycle.  This means 
that, all other things (fabrication technology, etc.) being equal, the 
PIC will requuire more power per instruciton to get the job done.

2) computing architecture.  The PIC has what I personally consider to be 
a very clumbsy architectural design.  The registerset usage is not 
orthogonal,  memroy addressing isn't linear, etc.  While PICs are 
imminently programmable (witness the massive nuymber of PICs in use, and 
the hughe number of hobbyist projects based on PICs), these 
architecturalk detailsmake them more difficult to program.  Some people 
seem to see the very small PIC instruction set as a plus.  I do not.

3) While there are a large number of different AVR processors avaiable, 
the PIC line swamps the AVR line in terms of numbers of family members. 
Moreover,  there can be fairly substantial differences in the way things 
are done from one PIC family to another.  Forthe most part, AVRs are 
AVRs. Within reasonable limits, what works on one AVR will work on 
another (exluding, of course, the use of hardware resources such as 
additional peripheral features in the larger, more powerful familky 
members).

4)  While some newer PIC support ISP (In System Programming) without 
specialized expensive hardware and software, many (most?) do not.  
Worse, the programming hardware that works for one PIC family may or may 
not work for the next more powerful family up the line, which can be a 
real headache if you discover that theprocessor you chose is lacking in 
some speed or hardware resource you need, and overlooked in your initial 
selection.

5)   **ALL** of the software you will need to develop a project on te 
AVR is freely available, including some stellar quality software 
directly from Atmel.  For the PIC line, you'll pretty muvch be limitewd 
to what you can purchase (though not exclusively).  I am not aware of an 
implmentation, for example, of gcc for the PIC, but it is out there for 
the AVR (primary reason for this, I suspect,is the complexity of 
supporting a wide range of PIC processors, with the massively differing 
hardware and software requirements).

6) back to the programming issiue a moment:  for about $5 (retail cost 
of components) you can easily construct a programming dongle usable with 
ANY AVR processor.  A DB-25M connector, 5 strands of wire, and a means 
of connecting the wires at the other end to the AVR (I saw oe guy who 
useed mini-alligator clips - not something I would recommend, however).  
I don't know of anyone who can put together a PIC programming platform 
for $5.

7)  Though I haven't searched exhaustively for PIC support, my 
experience in searching for AVR support onthe World Wide Web has been 
p[leasantand highly productive.  I wuld be verysurprised to see the 
level and scope of free web basedsupport for the PIC that I have found 
for the AVR family.

8)  IN terms of raw speed,  AVRs are availablew, in general, up to 20 
MIPs in performance.  PICs (with the exception of the dsPIC line) are 
restricted to 10 MIPs, max.  (there is one AVR that offers 48 MIPs 
performance, but it is a special unit, and I don't consider it fair to 
include it in this comparison(the AT76USB370, 48 Mhz clock, up to 12 
Mbps USB 2.0).

9)  Finally, and most importantly:  if you go with PIC, you  will not 
enjoy the benefits and pleasures of dealing with all of us, here in AVR 
land!!!!

tom